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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Tetrahedron. Author manuscript; available in PMC 2010 August 15.
Published in final edited form as:
Tetrahedron. 2009 August 15; 65(33): 6591–6599.
doi:  10.1016/j.tet.2009.02.065
PMCID: PMC2713043
NIHMSID: NIHMS99792

Synthesis and Preliminary Evaluation of Duocarmycin Analogues Incorporating the 1,2,11,11a-Tetrahydrocyclopropa[c]naphtho[2,3-e]indol-4-one (CNI) and 1,2,11,11a-Tetrahydrocyclopropa[c]naphtho[1,2-e]indol-4-one (iso-CNI) Alkylation Subunits

Abstract

Efficient syntheses and a preliminary evaluation of 1,2,11,11a-tetrahydrocyclopropa[c]-naphtho[2,3-e]indole (CNI) and 1,2,11,11a-tetrahydrocyclopropa[c]naphtho[1,2-e]indole (iso-CNI), and their derivatives containing an anthracene and phenanthrene variant of the CC-1065 or duocarmycin alkylation subunit are detailed.

Introduction

CC-1065 (1),1 the duocarmycins (23),24 and yatakemycin (4)5 are the parent members of a class of potent antitumor antibiotics that derive their properties through a sequence-selective alkylation of duplex DNA (Figure 1).6,7 Extensive studies have characterized their structural features responsible for the DNA alkylation reaction and have established fundamental relationships between their structure and reactivity or activity.611 Aside from the structural complexity inherent in the alkylation subunit, they possess a stability that defies intuition. This is due to the vinylogous amide conjugation and stabilization of the cyclohexadienone structure which is dominant over that activating the cross-conjugated cyclopropane.1214 Accordingly, disruption of this vinylogous amide conjugation leads to remarkable increases in reactivity as large as 104-fold14 that we have suggested is the source of catalysis for the DNA alkylation reaction.812

The synthesis of analogues containing deep-seated structural changes have been central to these studies providing insights not accessible through examination of the natural products themselves.15 The two most significant being the delineation of a fundamental parabolic relationship between reactivity and cytotoxic potency16,17 and that the catalysis for the DNA alkylation reaction likely entails a DNA binding induced conformation change that disrupts the alkylation subunit stabilizing vinylogous amide conjugation.8,9,12 Among the modified alkylation subunits introduced, the 1,2,9,9a-tetrahydrocyclopropa[c]benz[1,2-e]indol-4-one (CBI)18 alkylation subunit has emerged as the most extensively examined series, Figure 2. Not only is it the most synthetically19 accessible alkylation subunit in a rich series, but its derivatives exhibit biological properties18,20 that surpass those of 1 and 2 while approaching those of 3, and it exhibits a stability and inherent reaction regioselectivity that are near optimal.18

As an extension of these studies, we report herein two new classes of CBI-based agents that incorporate the extended anthracene and phenanthrene skeleton. Prospective modeling of the former linear 1,2,11,11a-tetrahydrocyclopropa[c]naphtho[2,3-e]indol-4-one (CNI) suggested that its derivatives may effectively bind DNA with its extended alkylation subunit productively enhancing catalysis of the DNA reaction, whereas the latter angular 1,2,11,11a-tetrahydrocyclopropa[c]naphtho[1,2-e]indol-4-one (iso-CNI) derivatives may suffer destabilizing steric interactions precluding effective DNA alkylation.

Results and Discussion

Synthesis

The synthesis of the CNI subunit began by condensation of commercially available aldehyde 11 with the known phosphonate21 to provide 12, and was followed by selective removal of the tert-butyl ester to provide the carboxylic acid 13 (Scheme 1). Friedel–Crafts cyclization effected by treatment with Ac2O and subsequent hydrolysis of the resulting acetate provided phenol 14 (61%, 2 steps). Benzyl protection of the phenol (77%) and LiOH hydrolysis of 15 gave 16 (100%). Treatment of 16 with the Shioiri–Yamada reagent (DPPA) in t-BuOH and subsequent Curtius rearrangement of the intermediate acyl azide provided the Boc protected amine 17 in 86%. Regioselective C4 bromination of 17 (74%) and subsequent N-alkylation of 18 with 1,3-dichloropropene afforded 19 (93%) and set the stage for a key 5-exo-trig aryl radical–alkene cyclization22 to provide 20. This latter cyclization was best effected in toluene (105 °C) and also served to reduce the C5 bromide that was used to direct the Friedel–Crafts cyclization of 13 to provide the linear anthracene skeleton versus the otherwise preferred phenanthrene skeleton.23 Resolution of 20 by chromatographic separation on a semiprep Chiralcel OD column provided both enantiomers cleanly which were then subjected to hydrogenolysis to provide 21 (natural S enantiomer shown). Spirocyclization of 21 was effected by treatment with DBU in anhydrous CH3CN to give N-Boc-CNI (22) in good yield (61%).

N-Boc deprotection of 21 and subsequent coupling of the amine hydrochloride salt with 5,6,7-trimethoxyindole-2-carboxylic acid (TMI) provided 23 (47%), which was spirocyclized to provide 24 (CNI-TMI) using DBU (60%, Scheme 2).

The synthesis of the iso-CNI subunit began by preparation of 26 following the modified Stobbe condensation previously described (Scheme 3). Selective removal of the tert-butyl ester, Friedel–Crafts cyclization to the phenanthrene effected by treatment with Ac2O, and hydrolysis of the resulting acetate provided phenol 27 (86% over 3 steps). Benzyl protection of 27 (95%) and LiOH hydrolysis of 28 gave the carboxylic acid 29 (96%), which was subjected to a modified Curtius rearrangement for conversion to the Boc-protected amine 30. Regioselective C4 bromination, subsequent N-alkylation with 1,3-dichloropropene, and 5-exo-trig aryl radical–alkene cyclization gave 33.24 Resolution of 33 by chromatographic separation on a semiprep Chiralcel OD column provided both enantiomers cleanly which were subjected to transfer hydrogenolysis to provide 34 (natural S enantiomer shown). Spirocyclization of 34 was effected by treatment with NaH to give N-Boc-iso-CNI (35) in good yield (54%).

Boc deprotection of 34 and subsequent coupling of the amine hydrochloride salt with 5,6,7-trimethoxyindole-2-carboxylic acid (TMI) provided 36 (57%), which was spirocyclized to provide 37 (iso-CNI-TMI) using DBU (60%), Scheme 4.

Solvolysis Reactivity

A key feature of the alkylation subunits is their intrinsic reactivity (stability) which correlates with the cytotoxic potency of the corresponding derivatives.16 Consequently, the solvolytic reactivity of both N-Boc-CNI (22) and N-Boc-iso-CNI (35) at pH 3 (50% buffer–MeOH, buffer = 0.1 M citric acid, 0.2 M Na2HPO4, and deionized H2O) was established and compared to that of the preceding analogues including N-Boc-CBI (Figure 3).18 Consistent with expectations and intrinsic to their structures, both N-Boc-CNI (t1/2 = 115 h) and N-Boc-iso-CNI (t1/2 = 146 h) exhibited the remarkable stability of N-Boc-CBI (t1/2 = 133 h) even at pH 3. Both were approximately four-times more stable than the alkylation subunit of CC-1065 (N-Boc-CPI, t1/2 = 36 h)25 and approach the stability of the alkylation subunit of duocarmycin SA and yatakemycin (N-Boc-DSA, t1/2 = 177 h).26,27

Figure 3
Solvolysis reactivity, pH = 3.

Cytotoxic Activity

The cytotoxic activity of the key CNI and iso-CNI derivatives was established against L1210, a leukemia cell line utilized extensively in past studies, Figure 4. Consistent with expectations based on their relative reactivity, the cytotoxic activity of both N-Boc-CNI (22) and CNI-TMI (24) proved nearly indistinguishable from the corresponding CBI derivative. Notably, (+)-CNI-TMI exhibited the exceptionally potent activity observed with (+)-CBI-TMI (IC50 = 30 pM), and the unnatural enantiomers were 10–100 fold less active. In contrast, the iso-CNI derivatives were >10-fold less active than either the CBI or CNI derivatives indicating that they exhibit a diminished cytotoxic activity relative to expectations based on their reactivity. Such observations are consistent with modeling studies that suggest they suffer from a less effective interaction with the minor groove of duplex DNA.

Figure 4
In vitro cytotoxic activity, L1210 (nM).

Conclusions

Efficient syntheses and a preliminary evaluation of 1,2,11,11a-tetrahydrocyclopropa[c]-naphtho[2,3-e]indole (CNI) and 1,2,11,11a-tetrahydrocyclopropa[c]naphtho[1,2-e]indole (iso-CNI), and their derivatives containing an anthracene and phenanthrene variant of the CC-1065 or duocarmycin alkylation subunit are detailed. Both were found to exhibit a reactivity comparable with the prototypical CBI derivatives, but only the former CNI derivatives exhibited the comparable cytotoxic activity. Further studies into the origin of the distinctions are in progress and will be reported in due course.

Experimental Section

4-tert-Butyl 1-Ethyl 2-(1-Bromonaphthalen-2-yl-methylene)butanedioate (12)

A solution of 4-tert-butyl 1-ethyl 2-(diethoxyphosphoryl)succinate21 (8.61 g, 25.4 mmol, 1.1 equiv) in THF (75 mL) was cooled to 0 °C and NaH (60% oil dispersion, 1.02 mg, 25.4 mmol, 1.1 equiv) was added in a single addition. The reaction mixture was gradually warmed to room temperature over 1 h. The mixture was cooled to 0 °C and a solution of 1-bromonaphthalene-2-carbaldehyde (5.43 g, 23.1 mmol) in THF (40 mL) was added and the mixture was warmed to room temperature and stirred for 16 h. The mixture was quenched with the addition of water (100 mL) and diluted with EtOAc (100 mL). The organic layer was washed with water (100 mL), saturated aqueous NaCl3 (100 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 4 × 12 cm, 0–10% EtOAc–hexanes) afforded 12 (6.62 g, 68%) as a yellow viscous oil: Rf = 0.49 (10% EtOAc–hexanes); 1H NMR (400 MHz, CDCl3) δ 8.34 (d, J = 8.9 Hz, 1H), 8.05 (s, 1H), 7.85–7.81 (m, 2H), 7.62 (dt, J = 1.4, 7.6 Hz, 1H), 7.56 (dt, J = 1.4, 7.5 Hz, 1H ), 7.40 (d, J = 8.4 Hz, 1H), 4.33 (q, J = 6.1 Hz, 2H), 3.32 (s, 2H), 1.46 (s, 9H), 1.38 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 170.0, 167.0, 141.5, 134.0, 133.8, 132.2, 128.5, 128.1, 127.8, 127.7, 127.20, 127.18, 126.5, 124.4, 81.0, 61.2, 35.1, 28.0 (3C), 14.2; IR (film) νmax 2977, 2948, 1725, 1720, 1367, 1256, 1152 cm−1; HRMALDI–FTMS (DHB) m/z 441.0679 (M + Na+, C21H23BrO4 requires 441.0672).

(E)-3-(Ethoxycarbonyl)-4-(1-bromonaphthalen-2-yl)but-3-enoic acid (13)

A solution of 12 (1.62 g, 3.87 mmol) in TFA (18 mL) was cooled to 0 °C and H2O (2 mL) was added. The reaction mixture was gradually warmed to room temperature over 2 h before the solvent was removed in vacuo, followed by azeotropic distillation with toluene (3 × 50 mL) until the TFA was completely removed. Flash chromatography (SiO2, 2.5 × 25 cm, 50–99% EtOAc–hexanes gradient) afforded 13 (1.20 g, 86%) as a white solid: mp 171–173 °C (dec); Rf = 0.30 (10% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.34 (d, J = 8.4 Hz, 1H), 8.13 (s, 1H), 7.86 (s, 1H), 7.85 (s, 1H), 7.64 (dt, J = 1.2, 7.6 Hz, 1H), 7.58 (dt, J = 1.0, 7.5 Hz, 1H), 7.41 (d, J = 8.4 Hz, 1H), 4.36 (q, J = 7.1 Hz, 2H), 3.46 (s, 2H), 1.39 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 176.9, 166.9, 142.7, 134.1, 133.3, 132.1, 128.2, 128.0, 127.9, 127.4, 127.2, 127.1, 126.3, 124.4, 61.5, 33.8, 14.2; IR (film) νmax 3226, 2950, 2919, 2847, 1707, 1461 cm−1; HRMALDI–FTMS (DHB) m/z 385.0049 (M + Na+, C17H15BrO4 requires 385.0046).

Ethyl 4-Acetoxy-9-bromoanthracene-2-carboxylate

A solution of 13 (800 mg, 2.21 mmol) in Ac2O (45 mL) was treated with NaOAc (480 mg, 11.05 mmol) and warmed at 110 °C for 20 h. The mixture was cooled and the solvent was removed in vacuo, followed by azeotropic distillation with toluene (3 × 50 mL) until the Ac2O was completely removed. Flash chromatography (SiO2, 3.5 × 16 cm, 6–16% EtOAc–hexanes gradient) afforded ethyl 4-acetoxyphenanthrene-2-carboxylate (170 mg, 25%) as a yellow film and the title compound (400 mg, 61%) as a yellow solid: mp 71–73 °C; Rf = 0.49 (10% EtOAc–hexanes); 1H NMR (400 MHz, CDCl3) δ 9.23 (s, 1H), 8.52 (d, J = 8.8 Hz, 1H), 8.43 (s, 1H), 8.00 (d, J = 8.4 Hz, 1H), 7.83 (s, 1H), 7.65 (t, J = 7.6 Hz, 1H), 7.57 (t, J = 7.5 Hz, 1H), 4.49 (q, J = 7.1 Hz, 2H), 2.56 (s, 3H), 1.48 (t, J = 7.1 Hz, 3H), 1.45 (t, J = 6.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 169.5, 166.1, 147.8, 134.4, 131.7, 131.0, 129.9, 129.4, 129.3, 128.2, 128.1, 127.5, 125.7, 121.4, 117.0, 104.2, 61.0, 20.7, 14.7; IR (film) νmax 2958, 1769, 1715, 1365, 1231, 1197 cm−1; HRMALDI–FTMS (DHB) m/z 409.0058 (M + Na+, C19H15BrO4 requires 409.0046).

For ethyl 4-acetoxyphenanthrene-2-carboxylate: yellow solid; 1H NMR (400 MHz, CDCl3) δ 9.01 (m, 1H), 8.20 (s, 1H), 7.91 (m, 1H), 7.75 (d, J = 7.7 Hz, 1H), 7.67 (d, J = 7.7 Hz, 1H), 7.61 (m, 4H), 4.41 (q, J = 6.4 Hz, 2H), 2.55 (s, 3H), 1.40 (t, J = 6.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 168.4, 166.3, 134.7, 133.0, 131.4, 129.9, 129.6, 129.5, 129.4, 127.3, 127.2, 127.1, 126.5, 115.8, 62.1, 22.0, 4.7; IR (film) νmax 1776, 1731, 1558, 1367, 1218, 1181, 1036 cm−1; HRMALDI–FTMS (DHB) m/z 331.0947 (M + Na+, C19H16O4 requires 331.0941).

Ethyl 9-Bromo-4-hydroxyanthracene-2-carboxylate (14)

A solution of ethyl 4-acetoxy-9-bromoanthracene-2-carboxylate (2.00 g, 5.18 mmol) in EtOH (52 mL) was treated with K2CO3 (787 mg, 5.70 mmol, 1.1 equiv) and the reaction mixture was stirred for 4 h at 23 °C. The mixture was diluted with EtOAc (50 mL), washed with saturated aqueous NH4Cl (100 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 4 × 30 cm, 0–10% EtOAc–hexanes gradient) afforded 14 (1.78 g, 100%) as a yellow solid: mp 197–199 °C; Rf = 0.28 (16% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.95 (s, 1H), 8.88 (s, 1H), 8.54 (d, J = 8.5 Hz, 1H), 8.07 (d, J = 8.5 Hz, 1H), 7.65 (t, J = 7.7 Hz, 1H), 7.58 (t, J = 7.7 Hz, 1H), 7.41 (s, 1H), 5.76 (br s, 1H), 4.49 (q, J = 7.0 Hz, 2H), 1.48 (t, J = 7.0 Hz, 3H); 1H NMR (400 MHz, DMSO-d6) δ 11.09 (s, 1H), 8.93 (s, 1H), 8.57 (s, 1H), 8.36 (dd, J = 0.8, 8.8 Hz, 1H), 8.23 (d, J = 8.5 Hz, 1H), 7.72 (dt, J = 1.2, 7.7 Hz, 1H), 7.61 (dt, J = 1.5, 7.5 Hz, 1H), 7.35 (d, J = 1.3 Hz, 1H), 4.39 (q, J = 7.1 Hz, 2H), 1.38 (t, J = 7.1 Hz, 3H); IR (film) νmax 3409, 2953, 1697, 1595, 1243, 1107, 1031 cm−1; HRMALDI–FTMS (DHB) m/z 344.0045 (M.+, C17H13BrO3 requires 344.0048).

Ethyl 4-Benzyloxy-9-bromoanthracene-2-carboxylate (15)

A solution of 14 (800 mg, 2.33 mmol) in DMF (23 mL) was treated with K2CO3 (354 mg, 2.56 mmol, 1.1 equiv) and after 5 min, BnBr (0.31 mL, 2.56 mmol, 1.1 equiv) was added. The mixture was stirred for 3.5 h at 23 °C, then diluted with EtOAc (50 mL) and washed with saturated aqueous NH4Cl (100 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 4 × 30 cm, 0–10% EtOAc–hexanes gradient) afforded 15 (777 mg, 1.78 mmol, 77%) as a yellow solid: mp 124–126 °C; Rf = 0.50 (16% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.87 (s, 1H), 8.84 (s, 1H), 8.47 (d, J = 8.8 Hz, 1H), 7.98 (d, J = 8.1 Hz, 1H), 7.62–7.58 (m, 3H), 7.53–7.40 (m, 5H), 5.34 (s, 2H), 4.50 (q, J = 7.0 Hz, 2H), 1.52 (t, J = 7.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 167.1, 155.0, 137.0, 133.2, 131.6, 130.4, 129.2, 129.1, 128.7, 128.2, 127.80, 127.77, 127.72, 126.9, 126.4, 124.4, 123.9, 122.3, 102.2, 71.0, 61.8, 14.9; IR (film) νmax 1717, 1653, 1558 cm−1; HRMALDI–FTMS (DHB) m/z 434.0529 (M.+, C24H19BrO3 requires 434.0512).

4-Benzyloxy-9-bromoanthracene-2-carboxylic acid (16)

A solution of 15 (220 mg, 0.507 mmol) in 3:1:1 (v/v/v) THF–MeOH–H2O (5 mL) was treated with LiOH (59 mg, 1.39 mmol, 5 equiv) and stirred for 2 h at 23 °C. 4 N HCl (10 mL) was added and the mixture was diluted with CH2Cl2 (25 mL). The organic layer was washed with H2O (3 × 10 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 1.5 × 12.7 cm, 50–100% EtOAc–hexanes gradient) afforded 16 (204 mg, 100%) as a yellow solid: mp 291–293 °C (dec); Rf = 0.32 (50% EtOAc–hexanes); 1H NMR (500 MHz, DMSO-d6) δ 13.40 (bs, 1H), 8.89 (s, 1H), 8.82 (s, 1H), 8.46 (d, J = 8.8 Hz, 1H), 8.32 (d, J = 8.5 Hz, 1H), 7.80–7.76 (m, 1H), 7.68–7.64 (m, 3H), 7.50 (m, 3H), 7.42–7.38 (m, 1H), 5.40 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 168.6, 155.6, 137.9, 133.7, 131.8, 131.4, 131.3, 131.0, 130.0, 129.4, 129.2, 129.0 (2C), 128.3, 128.2 (2C), 127.4, 124.6, 123.8, 123.1, 103.7, 71.4; IR (film) νmax 3410, 2921, 2850, 1685, 1558, 1435, 1324 cm−1; HRMALDI–FTMS (DHB) m/z 406.0212 (M.+, C22H15BrO3 requires 406.0205).

4-Benzyloxy-2-(tert-butyloxycarbonyl)amino-9-bromoanthracene (17)

A solution of 16 (50 mg, 0.123 mmol) in distilled t-BuOH (1.23 mL) was treated with distilled Et3N (18.0 μL, 0.129 mmol) and DPPA (26.5 μL, 0.123 mmol, 1 equiv). The mixture was heated at 80 °C for 20 h then cooled to room temperature and diluted with EtOAc (1 mL). The solution was washed with saturated aqueous NaHCO3 (2 × 10 mL), H2O (10 mL), and saturated aqueous NaCl (10 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 1 × 11 cm, 17% EtOAc–hexanes) afforded 17 (50.4 mg, 0.105 mmol, 86%) as an orange solid: mp 110–112 °C; Rf = 0.36 (16% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.83 (s, 1H), 8.43 (d, J = 8.4 Hz, 1H), 7.98 (d, J = 8.4 Hz, 1H), 7.88 (s, 1H), 7.59 (m, 3H), 7.41 (m, 4H), 7.33 (br s, 1H), 6.85 (s, 1H), 5.32 (s, 2H), 1.60 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 155.4, 152.7, 137.6, 136.5, 131.6, 131.4, 130.6, 129.3, 128.7, 128.2, 127.8, 127.6, 127.0, 124.7, 123.0, 121.9, 120.2, 105.3, 98.3, 80.9, 71.5, 28.4 (3C); IR (film) νmax 3323, 2974, 2923, 1697, 1635, 1425, 1235, 1154 cm−1; HRMALDI–FTMS (DHB) m/z 500.0834 (M + Na+, C26H24BrNO3 requires 500.0832).

4-Benzyloxy-2-(tert-butyloxycarbonyl)amino-1,9-dibromoanthracene (18)

A solution of 17 (25 mg, 0.052 mmol) in anhydrous THF (120 μL) at −78 °C was treated with anhydrous TsOH (1.0 mg, 0.0052 mmol, 0.1 equiv, dried at 50 °C under high vacuum overnight) in THF (20 μL). The solution was stirred for 5 min before NBS (9.3 mg, 0.052 mmol, dried over P2O5 overnight) was added. The vial was protected from light and allowed to stir at −78 °C for 3 h. The reaction mixture was warmed to 23 °C and diluted with saturated aqueous NaHCO3 (1 mL). The mixture was diluted with EtOAc (25 mL) and washed with saturated aqueous NaHCO3 (10 mL), H2O (10 mL), and saturated aqueous NaCl (10 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 1 × 11 cm, 0–7% EtOAc–hexanes gradient) afforded 2-(tert-butyloxycarbonyl)amino-4-hydroxy-1,9-dibromoanthracene (6.2 mg, 26%) as a tan solid and 18 (21.4 mg, 74%) as a yellow solid: Rf = 0.34 (10% EtOAc–hexanes); 1H NMR (400 MHz, CDCl3) δ 8.89 (s, 1H), 8.63 (d, J = 8.9 Hz, 1H), 8.08 (s, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.82 (s, 1H), 7.63–7.59 (m, 3H), 7.50–7.40 (m, 4H), 5.33 (s, 2H), 1.60 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 154.4, 152.6, 138.4, 136.2, 133.8, 130.6, 128.9, 128.7, 128.6, 128.3, 128.2, 128.1, 128.0, 125.6, 124.8, 122.5, 118.7, 98.4, 96.3, 81.4, 70.8, 28.3; IR (film) νmax 2923, 2841, 1728, 1615, 1548, 1467, 1348, 1231, 1149 cm−1; HRMALDI–FTMS (DHB) m/z 577.9929 (M + Na+, C26H23Br2NO3 requires 577.9937).

For 2-(tert-butyloxycarbonyl)amino-4-hydroxy-1,9-dibromoanthracene: orange solid; Rf = 0.30 (10% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.85 (s, 1H), 8.66 (d, J = 8.5 Hz, 1H), 8.07 (d, J = 7.7 Hz, 1H), 7.82 (t, J = 7.0 Hz, 1H), 7.72 (t, J = 7.0 Hz, 1H), 7.09 (s, 1H), 1.58 (s, 9H); IR (film) νmax 3374, 2985, 2912, 1743, 1666, 1605, 1462, 1253, 1149 cm−1.

2-[N-(tert-Butyloxycarbonyl)-N-(3-chloroprop-2-en-1-yl)amino]-4-benzyloxy-1,9-dibromoanthracene (19)

A solution of 18 (1.65 g, 2.96 mmol) in DMF (50 mL) was treated with Bu4NI (55 mg, 0.148 mmol) under Ar. The mixture was cooled to 0 °C and NaH (60% suspension in mineral oil, 296 mg, 7.40 mmol, 2.5 equiv) was added. The solution was stirred for 0.5 h and 1,3-dichloropropene (820 μL, 8.88 mmol, 3 equiv) was added. The vial was protected from light and allowed to stir at 0 °C for 2 h before being treated with saturated aqueous NaHCO3 (5 mL). The mixture was extracted with Et2O (3 × 25 mL), and the combined organic layers were washed with H2O (3 × 20 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 3 × 20 cm, 16% EtOAc–hexanes) afforded 19 (1.74 g, 2.75 mmol, 93%) as a yellow solid as a mixture of E- and Z-olefin isomers: mp 67–69 °C; Rf = 0.35 (10% EtOAc–hexanes); 1H NMR (500 MHz, acetone-d6) δ 9.07 (d, J = 4.4 Hz, 1H), 8.63 (d, J = 8.8 Hz, 1H), 8.12 (m, 1H), 7.71 (t, J = 7.7 Hz, 1H), 7.64 (m, 2H), 7.58 (t, J = 7.0 Hz, 1H), 7.47 (m, 2H), 7.40 (app t, J = 7.4 Hz, 1H), 7.04 (d, J = 16.0 Hz, 1H), 6.23 (m, 1H), 6.15 (m, 1H), 5.47 (m, 2H), 4.67 and 4.63 (two d, J = 6.3 and 5.8 Hz, 1H), 4.38–4.48 (m, 1H), 4.14 (m, 1H), 1.36 (s, 9H); IR (film) νmax 2923, 2851, 1697, 1610, 1462, 1369, 1262, 1153 cm−1; HRMALDI–FTMS (DHB) m/z 552.0801 (M+ − Br, C29H27BrClNO3 requires 552.0801).

5-(Benzyloxy)-3-(tert-butyloxycarbonyl)-1-(chloromethyl)-1,2-dihydronaphtho[2,3-e]indole 20)

A solution of 19 (78 mg, 0.123 mmol) in toluene (3 mL) was degassed with Ar and treated with AIBN (4 mg, 24.6 μmol, 0.2 equiv) and Bu3SnH (83 μL, 0.308 mmol, 2.5 equiv). A stream of Ar was bubbled through the solution for 10 min before the reaction vessel was closed and warmed at 105 °C for 3 h. The mixture was cooled to 23 °C and concentrated in vacuo. Flash chromatography (SiO2, 1 × 15 cm, 67% benzene–hexanes) afforded 20 (40 mg, 0.084 mmol, 69%) as a yellow solid: mp 152–154 °C; Rf = 0.31 (16% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 8.87 (s, 1H), 8.12 (s, 1H), 8.00 (d, J = 8.1 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.61 (br m, 2H), 7.48 (m, 4H), 7.42 (m, 2H), 5.35 (s, 2H), 4.32 (br m, 1H), 4.20 (app t, J = 9.9 Hz, 1H), 4.09 (m, 2H), 3.52 (app t, J = 10.5 Hz, 1H), 1.63 (s, 9H); IR (film) νmax 2964, 2920, 1699, 1621, 1571, 1454, 1404, 1363 1337, 1143 cm−1; HRMALDI–FTMS (DHB) m/z 496.1631 (M + Na+, C29H28ClNO3 requires 496.1650).

Resolution of 20

The enantiomers of 20 were resolved on a HPLC semipreparative Diacel Chiralcel OD column (10 μm, 2 × 25 cm) using 5% i-PrOH–hexane eluant (8 mL/min). The enantiomers eluted with retention times of 12.3 min (unnatural enantiomer) and 14.4 min (natural enantiomer, α = 1.17).

3-(tert-Butyloxycarbonyl)-1-(chloromethyl)-5-hydroxy-1,2-dihydro-3H-naphtho[2,3-e]indole (21, seco-N-Boc-CNI)

A solution of 20 (89 mg, 0.188 mmol) in THF (2 mL) was treated with a catalytic amount of 10% Pd/C (2 mg) and placed under 1 atm of H2. The mixture was stirred at 23 °C for 1.5 h, filtered through a Celite plug, and concentrated in vacuo. Flash chromatography (SiO2, 1 × 10 cm, 0–25% EtOAc/hexanes gradient) afforded 21 (72 mg, 100%) as a white solid: mp 187–188 °C (dec); Rf = 0.17 (16% EtOAc–hexanes); 1H NMR (500 MHz, CDCl3) δ 9.65 (d, J = 7.7 Hz, 1H), 7.92 (br s, 1H), 7.84 (d, J = 7.4 Hz, 1H), 7.75 (d, J = 8.8 Hz, 1H), 7.62 (t, J = 7.4 Hz, 1H), 7.57 (d, J = 8.8 Hz, 1H), 7.53 (t, J = 7.7 Hz, 1H), 4.29 (m, 1H), 4.14 (app t, J = 8.8 Hz, 1H), 4.00 (m, 1H), 3.92 (app d, J = 11 Hz, 1H), 3.45 (app t, J = 11 Hz, 1H), 1.66 (s, 9H); 13C NMR (125 MHz, acetone-d6) δ 157.4, 131.7, 130.8, 129.9, 128.8, 128.4, 127.4, 125.7, 121.7, 117.1, 115.6, 105.2, 102.4, 65.0, 53.4, 47.1, 28.9 (3C), 25.7; IR (film) νmax 3367, 2960, 2919, 1674, 1501, 1460, 1415, 1405, 1369, 1338, 1262, 1134 cm−1; HRMALDI–FTMS (DHB) m/z 383.1283 (M.+, C22H22ClNO3 requires 383.1283).

3-(tert-Butyloxycarbonyl)-1,2,11,11a-tetrahydrocyclopropa[c]naphtho[2,3-e]indol-4-one (22, N-Boc-CNI)

A sample of 21 (7.1 mg, 18.5 μmol) was dissolved in freshly distilled CH3CN (200 μL) under Ar. Anhydrous DBU (14 μL, 92.5 μmol) was added at 23 °C, and the mixture was stirred for 1 h. The reaction mixture was then concentrated under a stream of N2 and applied directly to PTLC (SiO2, 10 × 20 cm, 50% EtOAc/hexanes) to afford 22 (3.9 mg, 61%) as a white solid: mp 61–63 °C; Rf = 0.35 (50% EtOAc–hexanes); 1H NMR (400 MHz, CDCl3) δ 8.77 (s, 1H), 8.01 (d, J = 8.1 Hz, 1H), 7.78 (d, J = 8.0 Hz, 1H), 7.55 (dt, J = 1.4, 7.5 Hz, 1H), 7.48 (dt, J = 1.3, 7.5 Hz, 1H), 7.28 (s, 1H), 6.88 (br s, 1H), 4.05–4.04 (m, 2H), 2.90–2.85 (m, 1H), 1.64 (dd, J = 4.3, 7.7 Hz, 1H), 1.58 (s, 9H), 1.52 (t, J = 4.6 Hz, 1H); 13C NMR (100 MHz, acetone-d6) δ 186.4, 162.4, 153.3, 138.7, 136.7, 133.4, 132.8, 131.3, 129.8, 129.1, 128.6, 127.8, 122.1, 109.5, 84.1, 54.9, 31.6, 29.2 (2C), 25.4; IR (film) νmax 2977, 1723, 1614, 1382, 1256, 1160, 1140, 856, 748 cm−1; HRMALDI–FTMS (DHB) m/z 348.1600 (M + H+, C22H21NO3 requires 348.1594). (+)-22: [α]23D +80 (c 0.075, CHCl3); (−)-22: [α]23D –87 (c 0.11, CHCl3).

seco-CNI-TMI (23)

A sample of 21 (11.1 mg, 28.9 μmol) was treated with 4 N HCl/EtOAc (250 μL) and stirred at 23 °C for 1 h. The solvent was removed under a stream of N2 and dried under high vacuum for 30 min. The grey residue was dissolved in DMF (20 μL) and treated with 5,6,7-trimethoxyindole-2-carboxylic acid28 (8.0 mg, 31.8 μmol) and EDCI (16.7 mg, 86.8 μmol). The mixture was stirred under Ar at 23 °C for 18 h in the absence of light before the solvent was removed under a stream of N2. PTLC (SiO2, 20 × 20 cm, EtOAc) afforded 23 (7.1 mg, 47%) as a white solid: mp 243–245 °C (dec); Rf = 0.55 (50% EtOAc–hexanes); 1H NMR (500 MHz, acetone-d6) δ 10.38 (s, 1H), 8.29 (s, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.86 (m, 2H), 7.64 (t, J = 7.0 Hz, 1H), 7.56 (t, J = 7.0 Hz, 1H), 7.18 (s, 1H), 7.01 (s, 1H), 4.81 (m, 1H), 4.35 (m, 1H), 4.09 (m, 2H), 4.05 (s, 3H), 3.89 (s, 3H), 3.88 (s, 3H), 3.80 (dd, J = 8.8, 2.2 Hz, 1H); IR (film) νmax 3426, 2903, 1723, 1313 cm−1; HRMALDI–FTMS (DHB) m/z 517.1511 (M + H+, C29H25ClN2O5 requires 517.1525).

CNI-TMI (24)

A sample of 21 (7.1 mg, 13.7 μmol) was dissolved in freshly distilled CH3CN (140 μL) under Ar. Anhydrous DBU (10.5 μL, 68.7 μmol) was added at 23 °C, and the mixture was stirred for 1 h. The reaction mixture was then concentrated under a stream of N2 and applied directly to PTLC (SiO2, 10 × 20 cm, 50% EtOAc–hexanes) to afford 24 (4.0 mg, 60%) as a white solid: Rf = 0.55 (50% EtOAc–hexanes); 1H NMR (500 MHz, acetone-d6) δ 10.48 (br s, 1H), 9.99 (s, 1H), 8.10 (d, J = 8.5 Hz, 1H), 7.95 (d, J = 6.6 Hz, 1H), 7.66 (app t, J = 7.0 Hz, 1H), 7.56 (t, J = 7.0 Hz, 1H), 7.26 (d, J = 8.5 Hz, 1H), 7.16 (s, 1H), 7.11 (s, 1H), 6.96 (s, 1H), 4.68 (dd, J = 9.9, 5.5 Hz, 1H), 4.59 (d, J = 9.9 Hz, 1H), 4.02 (s, 3H), 3.87 (s, 6H), 3.33 (m, 1H), 1.97 (d, J = 4.4 Hz, 1H), 1.79 (t, J = 5.1 Hz, 1H); IR (film) νmax 3297, 2919, 2854, 1650, 1601, 1385, 1261, 1229, 1105, 1045 cm−1; HRMALDI–FTMS (DHB) m/z 481.1751 (M + H+, C29H24N2O5 requires 481.1758). (+)-24: [α]23D +160 (c 0.1, CHCl3); (−)-24: [α]23D −160 (c 0.1, CHCl3).

4-tert-Butyl 1-Ethyl 2-(Naphthalen-8-yl-methylene)butanedioate (26)

A solution of 4-tert-butyl 1-ethyl 2-(diethoxyphosphoryl)succinate21 (1.00 g, 3.0 mmol) in THF (10 mL) was cooled to 0 °C and NaH (60% oil dispersion, 79 mg, 3.3 mmol) was added in a single addition. The reaction mixture was gradually warmed to room temperature over 2 h before being recooled to 0 °C. A solution of 1-naphthaldehyde (462 mg, 3.0 mmol) in THF (5 mL) was added and the mixture was warmed to room temperature and stirred for 12 h. The mixture was diluted with EtOAc (100 mL), and washed with saturated aqueous NaHCO3 (100 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 2.5 × 25 cm, 0–5% EtOAc–hexanes gradient) afforded 26 (480 mg, 63%; typically 45–66%) as a yellow oil: 1H NMR (250 MHz, CDCl3) δ 8.35 (s, 1H), 7.97–7.86 (m, 3H), 7.58–7.41 (m, 4H), 4.37 (q, J = 6.9 Hz, 2H), 3.35 (s, 2H), 1.46 (s, 9H), 1.41 (t, J = 6.9 Hz 3H); HRMALDI–FTMS (DHB) m/z 363.1564 (M + Na+, C21H24O4 requires 363.1572).

Ethyl 1-Hydroxyphenanthrene-3-carboxylate (27)

A solution of 26 (220 mg, 0.65 mmol) in TFA (3 mL) was cooled to 0 °C and H2O (0.1 mL) was added. The reaction mixture was gradually warmed to room temperature over 2 h and the solvent was removed in vacuo, followed by azeotropic distillation with toluene (3 × 50 mL) until the TFA was completely removed. Ac2O (3.5 mL) and NaOAc (53 mg, 0.65 mmol) were added and the mixture was warmed at 70 °C for 8 h. The mixture was cooled and the solvent was removed in vacuo, followed by azeotropic distillation with toluene (3 × 50 mL) until the Ac2O was completely removed. The mixture was dissolved in EtOH (2.2 mL) and treated with K2CO3 (100 mg, 0.72 mmol) and the reaction mixture was stirred for 4 h at 23 °C. The mixture was diluted with EtOAc (50 mL), washed with saturated aqueous NH4Cl (100 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 2.5 × 25 cm, 5–20% EtOAc–hexanes gradient) afforded 27 (149 mg, 86%) as an off-white solid: 1H NMR (250 MHz, CDCl3) δ 9.00 (s, 1H), 8.73 (d, J = 7.7 Hz, 1H), 8.22 (d, J = 9.1 Hz, 1H), 7.93–7.81 (m, 3H), 7.72–7.60 (m, 2H), 6.79 (br s, 1H), 4.51 (q, J = 6.9 Hz, 2H), 1.49 (t, J = 6.9 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 167.3, 152.4, 132.3, 131.2, 130.4, 128.7, 128.5, 128.0, 127.1, 125.1, 123.3, 120.0, 117.6, 110.2, 61.5, 14.4; IR (film) νmax 3370, 2925, 1682, 1434, 1372, 1273, 1250, 1025, 825, 749 cm−1; HRMALDI–FTMS (DHB) m/z 266.0955 (M+, C17H14O3 requires 266.0943).

Ethyl 1-Benzyloxyphenanthrene-3-carboxylate (28)

A solution of 27 (400 mg, 1.5 mmol) in DMF (5 mL) was treated with K2CO3 (290 mg, 2.1 mmol) and Bu4NI (12 mg, 0.03 mmol) and after 5 min, BnBr (214 μL, 1.8 mmol) was added. The mixture was stirred for 10 h at 23 °C, then diluted with EtOAc (50 mL) and washed with saturated aqueous NH4Cl (100 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 4 × 30 cm, 2–20% EtOAc–hexanes gradient) afforded 28 (507 mg, 95%) as an off-white solid: 1H NMR (250 MHz, CDCl3) δ 9.08 (s, 1H), 8.78 (d, J = 8.4 Hz, 1H), 8.31 (d, J = 9.1 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.85 (d, J = 9.1 Hz, 1H), 7.73–7.58 (m, 5H), 7.49–7.38 (m, 3H), 5.35 (s, 2H), 4.50 (q, J = 7.3 Hz, 2H), 1.50 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 166.9, 154.9, 136.7, 132.2, 130.8, 130.3, 128.6, 128.5, 128.2, 128.0, 127.6, 127.0, 126.9, 126.2, 120.2, 117.9, 106.6, 70.5, 61.2, 14.4; IR (film) νmax 2894, 1713, 1272, 1026, 749 cm−1; HRMALDI–FTMS (DHB) m/z 357.1498 (M + H+, C24H20O3 requires 357.1491).

1-Benzyloxyphenanthrene-3-carboxylic acid (29)

A solution of 28 (299 mg, 0.84 mmol) in 3:1:1 (v/v/v) THF–MeOH–H2O (7.5 mL) was treated with LiOH (60 mg, 2.5 mmol) and stirred for 36 h at 23 °C. 4 N HCl (10 mL) was added and the mixture was diluted with CH2Cl2 (25 mL). The organic layer was washed with H2O (3 × 10 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 1.5 × 12.7 cm, 50–100% EtOAc–hexanes gradient) afforded 29 (264 mg, 96%) as an off-white solid: mp 266–269 °C (dec); 1H NMR (250 MHz, DMSO-d6) δ 8.99 (s, 1H), 8.82 (d, J = 6.6 Hz, 1H), 8.21 (d, J = 9.1 Hz, 1H), 8.06–8.02 (m, 1H), 7.99 (d, J = 9.1 Hz, 1H), 7.72 (app t, J = 9.1 Hz, 4H), 7.60 (d, J = 6.6 Hz, 2H), 7.47–7.36 (m, 2H), 5.41 (s, 2H); 13C NMR (125 MHz, DMSO-d6) δ 167.5, 154.4, 136.8, 131.8, 130.2, 129.6, 129.1, 128.7, 128.6, 128.5, 127.9, 127.5, 127.4, 125.3, 123.2, 119.6, 117.1, 107.0, 69.9; ESI (negative) m/z 327 (M − H, C22H15O3).

1-(Benzyloxy)-3-((tert-butyloxycarbonyl)amino)phenanthrene (30)

A solution of 29 (200 mg, 0.6 mmol) in distilled t-BuOH (11 mL) was treated with distilled Et3N (167 μL, 1.2 mmol) and DPPA (258 μL, 1.2 mmol). The mixture was heated at 80 °C for 9 h then cooled to room temperature and diluted with EtOAc (1 mL). The solution was washed with saturated aqueous NaHCO3 (2 × 10 mL), H2O (10 mL), and saturated aqueous NaCl (10 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 1 × 11 cm, 2–10% EtOAc–hexanes gradient) afforded 30 (183 mg, 76%) as an off-white solid: mp 180–182 °C; 1H NMR (500 MHz, CDCl3) δ 8.56 (d, J = 7.7 Hz, 1H), 8.21 (s, 1H), 8.19 (d, J = 8.8 Hz, 1H), 7.86 (d, J = 8.8 Hz, 1H), 7.62 (d, J = 9.1 Hz, 1H), 7.60–7.55 (m, 4H), 7.44 (app t, J = 7.7 Hz, 2H), 7.39–7.33 (m, 2H), 6.80 (br s, 1H), 5.23 (s, 2H), 1.59 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 155.6, 152.8, 137.3, 136.9, 132.6, 132.0, 129.5, 128.6, 128.5, 128.0, 127.5, 126.7, 126.1, 124.5, 123.3, 122.1, 120.3, 119.7, 80.7, 70.4, 28.4 (3C); IR (film) νmax 3297, 2975, 1690, 1581, 1540, 1509, 1266, 1157, 815, 748 cm−1; HRMALDI–FTMS (DHB) m/z 399.1835 (M+, C26H25NO3 requires 399.1834).

1-(Benzyloxy)-4-bromo-3-((tert-butyloxycarbonyl)amino)phenanthrene (31)

A solution of 30 (100 mg, 0.25 mmol) in THF (6 mL) at −78 °C was treated with TsOH (25 mg, 0.13 mmol) in THF (3 mL). NBS (50 mg, 0.28 mmol) was added and the vial was protected from light and allowed to stir at −78 °C for 1 h. The reaction mixture was warmed to 23 °C and diluted with saturated aqueous NaHCO3 (1 mL). The mixture was diluted with EtOAc (25 mL) and washed with saturated aqueous NaHCO3 (10 mL), H2O (10 mL), and saturated aqueous NaCl (10 mL). The organic layer was dried (Na2SO4) and concentrated in vacuo. Flash chromatography (SiO2, 4 × 20 cm, 2–5% EtOAc–hexanes gradient) afforded 31 (109 mg, 88%) as a white solid: 1H NMR (500 MHz, CDCl3) δ 9.67 (d, J = 7.7 Hz, 1H), 8.21 (s, 1H), 8.18 (d, J = 9.2 Hz, 1H), 7.82 (d, J = 7.7 Hz, 1H), 7.64 (br s, 1H), 7.59 (d, J = 8.8 Hz, 1H), 7.57–7.51 (m, 4H), 7.42–7.32 (m, 3H), 5.27 (s, 2H), 1.55 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 154.5, 152.7, 136.8, 136.6, 134.2, 129.8, 129.4, 128.6, 128.3, 128.1, 127.8, 127.4, 126.9, 125.8, 124.4, 122.0, 120.0, 101.3, 99.6, 81.2, 70.7, 28.4 (3C); IR (film) νmax 3405, 2912, 1733, 1600, 1523, 1482, 1221, 1149, 810, 749 cm−1; HRMALDI–FTMS (DHB) m/z 500.0845 (M + Na+, C26H24BrNO3 requires 500.0837).

For isomer (10 mg, 8%): 1H NMR δ 8.74–7.72 (m, 1H), 8.15 (d, J = 8.0 Hz, 1H), 8.04–7.85 (m, 4H), 7.74–7.38 (m, 6H), 7.03 (br s, 1H), 4.84 (t, J = 10.6 Hz, 2H), 1.67 (s, 9H); HRMALDI–FTMS (DHB) m/z 500.0843 (M + Na+, C26H24BrNO3 requires 500.0837).

3-[N-(tert-Butyloxycarbonyl)-N-(3-chloroprop-2-en-1-yl)amino]-1-(benzyloxy)-4-bromophenanthrene (32)

A solution of 31 (50 mg, 0.10 mmol) in DMF (0.8 mL) was cooled to 0 °C. NaH (60% suspension in mineral oil, 12 mg, 0.30 mmol) was added and the solution was stirred for 0.25 h. The mixture was warmed to room temperature and 1,3-dichloropropene (28 μL, 0.3 mmol) was added. The vial was protected from light and allowed to stir for 2 h before being treated with saturated aqueous NaHCO3 (5 mL). The mixture was extracted with Et2O (3 × 25 mL), and the combined organic layers were washed with H2O (3 × 20 mL), dried (Na2SO4), and concentrated in vacuo. Flash chromatography (SiO2, 3 × 20 cm, 16% EtOAc–hexanes) afforded 32 (63 mg, 96%) as a yellow oil and as a mixture of E- and Z-olefin isomers: 1H NMR (250 MHz, CDCl3) δ 9.93 (d, J = 6.6 Hz, 1H), 8.32 (d, J = 9.1 Hz, 1H), 7.91–7.89 (m, 1H), 7.78 (d, J = 9.1 Hz, 1H), 7.64 (d, J = 6.2 Hz, 2H), 7.56–7.52 (m, 2H), 7.48–7.35 (m, 4H), 7.00 (d, J = 8.0 Hz, 1H), 6.92 (d, J = 13.2 Hz, 1H), 6.17–5.97 (m, 1H), 5.29 (app t, J = 6.2 Hz, 2H), 4.64–4.54 (m, 1H), 4.34 (dd, J = 15.7, 5.1 Hz, 1H), 3.83 (dd, J = 15.0, 7.7 Hz, 1H), 1.35 (s, 9H); IR (film) νmax 2973, 2921, 1701, 1591, 1368, 1165, 753 cm−1.

5-(Benzyloxy)-3-(tert-butyloxycarbonyl)-1-(chloromethyl)-1,2-dihydronaphtho[1,2-e]indole (33)

A solution of 32 (20 mg, 40 μmol) in C6H6 (2 mL) was degassed by three freeze–pump–thaw cycles and treated with AIBN (1 mg, 6 μmol) and Bu3SnH (13 μL, 50 μmol). A stream of Ar was bubbled through the solution for 10 min before the reaction vessel was closed and warmed to 80 °C for 15 h after which an additional amount of Bu3SnH (13 μL, 50 μmol) and AIBN (1 mg, 6 μmol) were added. The mixture was stirred for 3 h at 80 °C before being cooled to 23 °C and concentrated in vacuo. Flash chromatography (SiO2, 3 × 20 cm, 2–10% EtOAc/hexanes gradient) afforded 33 (9 mg, 48%) as an off-white solid: 1H NMR (500 MHz, CDCl3) δ 8.06 (d, J = 8.8 Hz, 1H), 7.93 (d, J = 7.0 Hz, 1H), 7.81 (d, J = 8.0 Hz, 1H), 7.62 (app t, J = 7.7 Hz, 1H), 7.59–7.53 (m, 4H), 7.45 (app t, J = 7.0 Hz, 2H), 7.38–7.36 (m, 1H), 5.30 (s, 2H), 4.59 (t, J = 9.2 Hz, 1H), 4.39 (d, J = 8.8 Hz, 1H), 4.16 (t, J = 9.7 Hz, 1H), 3.92 (d, J = 11.4 Hz, 1H), 3.36 (t, J = 11.0 Hz, 1H), 1.62 (s, 9H); IR (film) νmax 3467, 2950, 1700, 1644, 1366, 1239, 1163, 1138, 833 cm−1.

seco-N-Boc-iso-CNI (34)

A solution of 33 (20 mg, 0.04 mmol) in 3:1 (v/v) THF–MeOH (10 mL) was treated with a catalytic amount of 10% Pd/C (20 mg) and 25% aqueous HCO2NH4 (640 μL, 1.0 mmol). The mixture was stirred at 23 °C for 48 h, filtered through a Celite plug, and concentrated in vacuo. Flash chromatography (SiO2, 1 × 10 cm, 10–20% EtOAc–hexanes gradient) afforded 34 (15 mg, 90%) as a yellow oil: 1H NMR (500 MHz, CDCl3) δ 8.59 (d, J = 8.5 Hz, 1H), 8.17 (d, J = 9.2 Hz, 1H), 7.99 (br s, 1H), 7.91 (d, J = 8.1 Hz, 1H), 7.62 (t, J = 7.0 Hz, 1H), 7.61 (m, 3H), 6.51 (br s, 1H), 4.56 (app t, J = 8.5 Hz, 1H), 4.35 (d, J = 10.5 Hz, 1H), 4.14 (m, 1H), 3.90 (d, J = 10.5 Hz, 1H), 3.35 (t, J = 11.0 Hz, 1H), 1.63 (s, 9H); IR (film) νmax 3349, 2922, 1704, 1596, 1414, 1342, 1254, 1140, 747 cm−1; ESI (negative) m/z 382 (M − H, C22H21ClNO3).

Resolution of 34

The enantiomers of 34 were resolved on a HPLC semipreparative Diacel Chiralcel OD column (10 μm, 2 × 25 cm) using 5% i-PrOH–hexane eluant (8 mL/min). The enantiomers eluted with retention times of 18.5 min (natural enantiomer) and 13.9 min (unnatural enantiomer, α = 1.33). (1S)-34: [α]23D −50 (c 0.01, THF); (1R)-34: [α]23D +50 (c 0.01, THF).

3-(tert-Butyloxycarbonyl)-1,2,11,11a-tetrahydrocyclopropa[c]naphtho[1,2-e]indol-4-one (N-Boc-iso-CNI, 35)

A sample of 34 (2 mg, 5 μmol) was dissolved in 3:1 (v/v) THF–DMF (250 μL) under Ar and cooled to 0 °C. NaH (60% suspension in mineral oil, 600 μg, 15 μmol) was added and the mixture was stirred for 30 min. At this time, the reaction was quenched with the addition of pH 7.0 phosphate buffer (300 μL) and diluted with H2O (1 mL) and EtOAc (5 mL). The organic layer was collected, dried (Na2SO4), and concentrated in vacuo. PTLC (SiO2, 10 × 20 cm, 10% EtOAc–hexanes) afforded 35 (1.0 mg, 54%) as a white solid: 1H NMR (600 MHz, CDCl3) δ 8.56 (d, J = 8.3 Hz, 1H), 8.07 (s, 1H), 7.82–7.79 (m, 1H), 7.70–7.65 (m, 3H), 6.91 (s, 1H), 3.72 (d, J = 7.5 Hz, 1H), 3.65 (m, 2H), 1.47 (s, 9H), 0.92 (t, J = 7.5 Hz, 1H), 0.88–0.87 (m, 1H); HRMALDI–FTMS (DHB) m/z 348.1600 (M + H+, C22H21NO3 requires 348.1594). (+)-35: [α]23D +75 (c 0.1, CHCl3); (−)-35: [α]23D −75 (c 0.1, CHCl3).

seco-iso-CNI-TMI (36)

A sample of 35 (1.55 mg, 5.5 μmol) was treated with 4 N HCl/EtOAc (100 μL) and stirred at 23 °C for 1 h. The solvent was removed under a stream of N2 and dried under high vacuum for 30 min. The grey residue was dissolved in DMF (60 μL) and treated with 5,6,7-trimethoxyindole-2-carboxylic acid28 (1.37 mg, 5.5 μmol) and EDCI (3.15 mg, 16 μmol). The mixture was stirred under Ar at 23 °C for 18 h in the absence of light before the solvent was removed under a stream on N2. PTLC (SiO2, 20 × 20 cm, 50% EtOAc–hexanes) afforded 36 (1.6 mg, 57%) as a white solid: 1H NMR (500 MHz, CDCl3) δ 9.73 (br s, 1H), 9.51 (s, 1H), 8.68 (s, 1H), 8.33 (d, J = 8.8 Hz, 1H), 8.29 (d, J = 7.4 Hz, 1H), 7.94 (d, J = 7.4 Hz, 1H), 7.68 (d, J = 8.8 Hz, 1H), 7.60 (t, J = 7.4 Hz, 1H), 7.54 (t, J = 7.4 Hz, 1H), 6.74 (s, 1H), 6.54 (s, 1H), 4.71 (app d, J = 9.9 Hz, 1H), 4.60 (app t, J = 8.1 Hz, 1H), 4.46 (m, 1H), 4.18 (s, 3H), 4.00 (s, 3H), 3.87 (s, 3H), 3.69 (m, 1H), 3.24 (t, J = 11.4 Hz, 1H); IR (film) νmax 3411, 2959, 1591, 1454, 1412, 1318, 1260, 1107, 1050, 803 cm−1; HRMALDI–FTMS (DHB) m/z 516.1430 (M+, C29H25ClN2O5 requires 516.1452). (1S)-36: [α]23D +17 (c 2.0, CH2Cl2); (1R)-36: [α]23D −17 (c 1.0, CH2Cl2).

iso-CNI-TMI (37)

A sample of 36 (7.1 mg, 13.7 μmol) was dissolved in freshly distilled CH3CN (140 μL) under Ar. Anhydrous DBU (10 μL, 68 μmol) was added at 23 °C, and the mixture was stirred for 1 h. The reaction mixture was then concentrated under a stream of N2 and applied directly to PTLC (SiO2, 10 × 20 cm, 50% EtOAc–hexanes) to afford 37 (4.0 mg, 60%) as a white solid: 1H NMR δ 10.50 (br s, 1H), 8.55 (d, J = 8.2 Hz, 1H), 8.06 (s, 1H), 7.85–7.80 (m, 1H), 7.70–7.65 (m, 3H), 7.17 (s, 1H), 6.04 (s, 1H), 6.90 (s, 1H), 4.18 (s, 3H), 4.00 (s, 3H), 3.85(s, 3H), 3.70 (d, J = 7.5 Hz, 1H), 3.65 (m, 2H), 0.90 (s, J = 7.5 Hz, 1H); HRMALDI–FTMS (DHB) m/z 481.1759 (M + H+, C29H24N2O5 requires 481.1758). (+)-37: [α]23D +125 (c 0.1, THF); (−)-37: [α]23D −120 (c 0.1, THF).

Aqueous Solvolysis Reactivity: pH 3

Compounds 22 and 35 (50 μg) were dissolved in CH3OH (1.5 mL) and mixed with pH 3 aqueous buffer (1.5 mL). The buffer contained 4:1:20 (v:v:v) 0.1 M citric acid, 0.2 M Na2HPO4, and deionized H2O, respectively. Immediately after mixing, the UV spectra of the solution was measured against a reference solution containing CH3OH (1.5 mL) and the aqueous buffer (1.5 mL), and this reading was used as the initial absorbance value. The solution was stoppered, protected from light, and allowed to stand at 25 °C. The UV spectra were recorded at regular intervals until a constant value was obtained for the long-wavelength absorbance. The increase of the absorbance at 230 nm was monitored. The solvolysis rate constants for were determined from the slope of the line obtained from the least-squares treatment (r2 = 0.98) of the plot of ln[(AfAi)/(AfA)] versus time.

Acknowledgments

We gratefully acknowledge the financial support of NIH (CA41986) and the Skaggs Institute for Chemical Biology. KSM is a Skaggs fellow.

Footnotes

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