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Acta Crystallogr Sect E Struct Rep Online. 2008 June 1; 64(Pt 6): o1112.
Published online 2008 May 17. doi:  10.1107/S1600536808014372
PMCID: PMC2961627

N-(Fluoren-9-ylmethoxy­carbon­yl)-l-leucine

Abstract

The title compound [systematic name: fluoren-9-yl N-(1-carb­oxy-3-methyl­butyl)carbamate], C21H23NO4, exhibits torsion angles that vary from the typical values found in other Fmoc-protected amino acids, viz. the orientations of the fluorene and carboxyl groups [C—O—C—C = 93.8 (2) and N—C—C=O = −23.6 (2)°]. The crystal structure exhibits two inter­molecular hydrogen bonds (O—H(...)O and N—H(...)O) that link the mol­ecules into two-dimensional sheets parallel to the ab plane.

Related literature

For related literature on the structures of N-α-Fmoc-protected amino acids, see: Valle et al. (1984 [triangle]); Yamada et al. (2008 [triangle]).

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Object name is e-64-o1112-scheme1.jpg

Experimental

Crystal data

  • C21H23NO4
  • M r = 353.40
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-64-o1112-efi1.jpg
  • a = 5.4953 (1) Å
  • b = 14.2700 (3) Å
  • c = 24.3759 (6) Å
  • V = 1911.51 (7) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.09 mm−1
  • T = 150 K
  • 0.40 × 0.08 × 0.06 mm

Data collection

  • Rigaku AFC-8 diffractometer with Saturn70 CCD detector
  • Absorption correction: none
  • 40257 measured reflections
  • 3207 independent reflections
  • 2906 reflections with I > 2σ(I)
  • R int = 0.055

Refinement

  • R[F 2 > 2σ(F 2)] = 0.039
  • wR(F 2) = 0.111
  • S = 1.09
  • 3207 reflections
  • 327 parameters
  • All H-atom parameters refined
  • Δρmax = 0.27 e Å−3
  • Δρmin = −0.26 e Å−3

Data collection: CrystalClear (Rigaku/MSC, 2005 [triangle]); cell refinement: HKL-2000 (Otwinowski & Minor, 1997 [triangle]); data reduction: HKL-2000; program(s) used to solve structure: SIR2004 (Burla et al., 2005 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 [triangle]); software used to prepare material for publication: SHELXL97.

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808014372/fl2198sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808014372/fl2198Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

KY thanks the Ministry of Education, Science, Sports, Culture, and Technology (MEXT) of Japan for funding this work [Young Scientists (B), 20750022].

supplementary crystallographic information

Comment

The fluoren-9-ylmethoxycarbonyl (Fmoc) group is currently one of the most frequently used protecting groups for peptide synthesis since rapid cleavages can be readily achieved under mild basic conditions with racemization-free results. Almost all the Fmoc-protected twenty-L-amino acids are commercially available. The crystal structures of N-α-Fmoc-protected-L-alanine monohydrate (II, Valle et al., 1984) and L-serine (III, Yamada et al., 2008) have been reported so far. In the present study, we have carried out the crystal structure analysis of N-α-Fmoc-L-leucine, (I).

The bond distances and bond angles of (I, Fig. 1) are consistent with the typical values of Fmoc-protected amino acids found in the other crystal structures. Some torsion angles, however, are found to be quite different. The torsion angle of O2—C6—C1—N1, for example, is -23.6 (2)°, which is in disagreement with the previous observations in the Fmoc-protected amino acids in which the corresponding angles are 150.6° and 175.8° for (II) (Valle et al., 1984) and (III) (Yamada et al., 2008), respectively. Another example is that the torsion angle of C6—C1—N1—C7 in (I) is found to be -134.51 (15)°, which is in reasonable agreement with that of (II), -151.6°, but is inconsistent with that found in (II), -65.6°. Each angle between the fluorene ring and the NC(δb O)O plane is found to be different among the three Fmoc-protected amino acids. The torsion angles C7—O4—C8—C9 and O4—C8—C9—C10 for the title compound, for instance, are 93.78 (16)° and 60.54 (17)°, respectively. On the other hand, the corresponding angles are -179.7° and -172.1°, and 121.9° and -68.2° for (II) and (III), respectively.

Crystals of (I) contain two intermolecular hydrogen bonds (Table 1), which are formed between the carboxyl (O2—H2H) and amide oxygens (O3), and between the amide (N1—H1N) and the carbonyl (O1). The molecules are linked by O2—H2H···O3 hydrogen bonds to form a chain structure along the b axis. The linkage is supported by an additional C—H···O interaction (C8—H8A···O1). The chains are joined together by the N1—H1N···O1 hydrogen bonds to form a sheet structure parallel to the ab plane. The Fmoc and i-butyl moieties are packed between the sheets (Fig. 2).

Experimental

A powdered sample (I) was obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan) and was used for crystallization without further purifications. Colourless needle like crystals of (I) were slowly grown from a saturated dichloromethane solution.

Refinement

All H atoms were found in difference maps an refined with isotropic thermal parameters.

Figures

Fig. 1.
A view of the molecular structure of (I), showing the atom labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.
Fig. 2.
A packing diagram of (I) viewed. The hydrogen atoms were omitted for clarity, except for those forming the hydrogen bonds. Broken lines indicate the hydrogen bonds.

Crystal data

C21H23NO4F000 = 752
Mr = 353.40Dx = 1.228 Mg m3
Orthorhombic, P212121Mo Kα radiation λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 40402 reflections
a = 5.49530 (10) Åθ = 2.2–30.0º
b = 14.2700 (3) ŵ = 0.09 mm1
c = 24.3759 (6) ÅT = 150 K
V = 1911.51 (7) Å3Needle, colourless
Z = 40.40 × 0.08 × 0.06 mm

Data collection

Rigaku AFC-8 diffractometer with Saturn70 CCD detector3207 independent reflections
Radiation source: fine-focus rotating anode2906 reflections with I > 2σ(I)
Monochromator: confocalRint = 0.055
Detector resolution: 28.5714 pixels mm-1θmax = 30.0º
T = 150 Kθmin = 2.2º
ω scansh = −7→7
Absorption correction: nonek = −20→20
40257 measured reflectionsl = −34→34

Refinement

Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.039All H-atom parameters refined
wR(F2) = 0.111  w = 1/[σ2(Fo2) + (0.0687P)2 + 0.1717P] where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max < 0.001
3207 reflectionsΔρmax = 0.27 e Å3
327 parametersΔρmin = −0.25 e Å3
Primary atom site location: structure-invariant direct methodsExtinction correction: none

Special details

Experimental. All Friedel pairs were merged, and all f''s of containing atoms were set to zero.
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
O1−0.3755 (2)0.42665 (9)0.27853 (7)0.0421 (3)
O20.0123 (2)0.47101 (9)0.26982 (7)0.0455 (4)
H2H−0.047 (5)0.526 (2)0.2667 (11)0.055 (7)*
O30.1016 (2)0.15166 (8)0.23545 (6)0.0360 (3)
O40.4680 (2)0.22208 (8)0.22403 (5)0.0306 (2)
N10.1792 (2)0.29706 (9)0.26957 (6)0.0284 (3)
H1N0.280 (5)0.3438 (18)0.2738 (9)0.044 (6)*
C1−0.0651 (3)0.31083 (10)0.29096 (7)0.0287 (3)
H1−0.171 (4)0.2659 (15)0.2718 (9)0.035 (5)*
C2−0.0783 (4)0.29621 (13)0.35339 (8)0.0406 (4)
H2A0.047 (5)0.3372 (19)0.3712 (10)0.048 (7)*
H2B−0.225 (6)0.322 (2)0.3692 (13)0.065 (8)*
C3−0.0497 (4)0.19389 (13)0.37135 (8)0.0413 (4)
H30.102 (5)0.1685 (18)0.3516 (10)0.048 (7)*
C4−0.2695 (5)0.13470 (17)0.35502 (14)0.0601 (7)
H4A−0.312 (6)0.1369 (19)0.3131 (11)0.060 (8)*
H4B−0.387 (8)0.163 (3)0.3755 (15)0.088 (11)*
H4C−0.262 (6)0.065 (2)0.3677 (13)0.072 (9)*
C50.0014 (9)0.18903 (19)0.43291 (10)0.0705 (9)
H5A0.163 (8)0.227 (3)0.4437 (15)0.093 (12)*
H5B0.017 (6)0.124 (2)0.4463 (11)0.060 (8)*
H5C−0.127 (7)0.223 (2)0.4509 (13)0.072 (9)*
C6−0.1606 (3)0.40869 (10)0.27831 (7)0.0299 (3)
C70.2373 (3)0.21843 (10)0.24241 (6)0.0261 (3)
C80.5484 (3)0.14752 (11)0.18786 (6)0.0289 (3)
H8A0.476 (5)0.0932 (16)0.1976 (9)0.034 (5)*
H8B0.721 (5)0.1412 (15)0.1960 (9)0.034 (5)*
C90.5153 (3)0.17588 (11)0.12778 (7)0.0291 (3)
H90.337 (5)0.1858 (16)0.1193 (9)0.043 (6)*
C100.6613 (3)0.26233 (11)0.11325 (7)0.0308 (3)
C110.6335 (4)0.35445 (12)0.13131 (8)0.0385 (4)
H110.504 (5)0.3707 (16)0.1573 (9)0.035 (5)*
C120.8001 (4)0.42145 (13)0.11327 (9)0.0456 (4)
H120.783 (5)0.4852 (19)0.1253 (10)0.054 (7)*
C130.9889 (4)0.39782 (15)0.07795 (8)0.0459 (5)
H131.117 (5)0.4495 (19)0.0642 (11)0.057 (7)*
C141.0166 (4)0.30626 (15)0.05954 (8)0.0408 (4)
H141.148 (5)0.2884 (16)0.0338 (10)0.048 (6)*
C150.8514 (3)0.23871 (12)0.07728 (7)0.0323 (3)
C160.8333 (3)0.13832 (12)0.06424 (6)0.0329 (3)
C170.9738 (4)0.08170 (16)0.03029 (8)0.0437 (4)
H171.114 (5)0.1107 (17)0.0111 (10)0.048 (7)*
C180.9091 (5)−0.01199 (16)0.02442 (8)0.0505 (5)
H181.003 (6)−0.0545 (19)0.0001 (11)0.060 (7)*
C190.7076 (5)−0.04829 (14)0.05165 (8)0.0473 (5)
H190.671 (5)−0.1136 (19)0.0461 (10)0.053 (7)*
C200.5670 (4)0.00808 (12)0.08599 (8)0.0392 (4)
H200.423 (5)−0.0159 (18)0.1060 (11)0.053 (7)*
C210.6305 (3)0.10141 (11)0.09189 (6)0.0317 (3)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O10.0236 (6)0.0258 (5)0.0769 (9)0.0009 (4)0.0034 (6)−0.0057 (6)
O20.0258 (6)0.0197 (5)0.0910 (11)−0.0004 (4)−0.0005 (7)0.0087 (6)
O30.0236 (5)0.0220 (5)0.0623 (7)−0.0025 (4)0.0012 (5)−0.0085 (5)
O40.0245 (5)0.0259 (5)0.0415 (6)−0.0027 (4)0.0051 (5)−0.0058 (4)
N10.0232 (6)0.0190 (5)0.0430 (7)−0.0026 (5)0.0012 (5)−0.0035 (5)
C10.0246 (7)0.0194 (6)0.0423 (8)−0.0004 (5)0.0036 (6)−0.0008 (5)
C20.0521 (11)0.0276 (7)0.0422 (8)0.0008 (8)0.0104 (8)0.0005 (6)
C30.0447 (10)0.0325 (8)0.0466 (9)0.0005 (8)0.0056 (8)0.0076 (7)
C40.0468 (13)0.0424 (11)0.0911 (19)−0.0093 (10)0.0005 (13)0.0225 (12)
C50.115 (3)0.0485 (12)0.0480 (11)0.0009 (17)0.0066 (16)0.0115 (10)
C60.0243 (7)0.0214 (6)0.0440 (8)−0.0003 (5)0.0012 (6)−0.0026 (5)
C70.0229 (6)0.0204 (6)0.0351 (7)0.0002 (5)−0.0014 (5)0.0006 (5)
C80.0270 (7)0.0235 (6)0.0361 (7)0.0019 (6)0.0027 (6)−0.0013 (5)
C90.0249 (7)0.0254 (7)0.0370 (7)−0.0001 (6)−0.0018 (6)−0.0007 (5)
C100.0282 (8)0.0287 (7)0.0353 (7)−0.0019 (6)−0.0020 (6)0.0030 (6)
C110.0407 (10)0.0293 (8)0.0455 (9)−0.0012 (7)0.0029 (8)0.0011 (6)
C120.0529 (12)0.0301 (8)0.0537 (10)−0.0085 (9)0.0003 (10)0.0034 (7)
C130.0463 (11)0.0412 (10)0.0500 (10)−0.0140 (9)−0.0004 (9)0.0089 (8)
C140.0346 (9)0.0490 (10)0.0389 (8)−0.0064 (8)0.0021 (7)0.0082 (7)
C150.0305 (8)0.0338 (7)0.0326 (7)−0.0004 (6)−0.0026 (6)0.0037 (6)
C160.0325 (8)0.0364 (8)0.0296 (6)0.0047 (7)−0.0040 (6)0.0006 (6)
C170.0427 (10)0.0523 (11)0.0360 (8)0.0134 (9)−0.0003 (8)−0.0033 (7)
C180.0625 (14)0.0489 (11)0.0401 (9)0.0206 (11)−0.0069 (9)−0.0108 (8)
C190.0671 (14)0.0341 (9)0.0406 (8)0.0092 (9)−0.0122 (10)−0.0079 (7)
C200.0483 (11)0.0299 (8)0.0395 (8)−0.0001 (8)−0.0082 (8)−0.0026 (6)
C210.0330 (8)0.0298 (7)0.0324 (7)0.0042 (6)−0.0060 (6)−0.0021 (6)

Geometric parameters (Å, °)

O1—C61.208 (2)C8—H8B0.97 (2)
O2—C61.318 (2)C9—C101.514 (2)
O2—H2H0.85 (3)C9—C211.515 (2)
O3—C71.2217 (18)C9—H91.01 (3)
O4—C71.3460 (19)C10—C111.395 (2)
O4—C81.4506 (18)C10—C151.405 (2)
N1—C71.3413 (18)C11—C121.395 (3)
N1—C11.453 (2)C11—H110.98 (2)
N1—H1N0.87 (3)C12—C131.390 (3)
C1—C61.523 (2)C12—H120.96 (3)
C1—C21.538 (2)C13—C141.390 (3)
C1—H10.98 (2)C13—H131.07 (3)
C2—C31.532 (3)C14—C151.393 (3)
C2—H2A1.00 (3)C14—H140.99 (3)
C2—H2B0.96 (3)C15—C161.471 (2)
C3—C41.527 (3)C16—C171.391 (3)
C3—C51.528 (3)C16—C211.405 (3)
C3—H31.03 (3)C17—C181.391 (3)
C4—H4A1.05 (3)C17—H170.99 (3)
C4—H4B0.91 (4)C18—C191.391 (4)
C4—H4C1.04 (3)C18—H180.99 (3)
C5—H5A1.08 (4)C19—C201.395 (3)
C5—H5B0.98 (3)C19—H190.96 (3)
C5—H5C0.96 (4)C20—C211.384 (2)
C8—C91.530 (2)C20—H200.99 (3)
C8—H8A0.90 (2)
C6—O2—H2H111.1 (19)C9—C8—H8B109.5 (13)
C7—O4—C8117.44 (12)H8A—C8—H8B107 (2)
C7—N1—C1120.66 (13)C10—C9—C21102.41 (13)
C7—N1—H1N123.1 (16)C10—C9—C8112.11 (13)
C1—N1—H1N116.1 (16)C21—C9—C8108.51 (13)
N1—C1—C6111.69 (13)C10—C9—H9110.6 (13)
N1—C1—C2112.36 (15)C21—C9—H9112.6 (13)
C6—C1—C2107.96 (13)C8—C9—H9110.4 (13)
N1—C1—H1106.7 (13)C11—C10—C15120.30 (16)
C6—C1—H1107.3 (13)C11—C10—C9129.51 (16)
C2—C1—H1110.7 (13)C15—C10—C9110.16 (14)
C3—C2—C1114.03 (14)C10—C11—C12118.34 (19)
C3—C2—H2A111.3 (15)C10—C11—H11120.5 (13)
C1—C2—H2A108.5 (14)C12—C11—H11121.1 (13)
C3—C2—H2B109.2 (18)C13—C12—C11121.27 (19)
C1—C2—H2B112.6 (18)C13—C12—H12119.4 (17)
H2A—C2—H2B100 (2)C11—C12—H12119.3 (17)
C4—C3—C5112.1 (2)C14—C13—C12120.65 (18)
C4—C3—C2111.80 (19)C14—C13—H13118.2 (15)
C5—C3—C2110.04 (18)C12—C13—H13121.1 (14)
C4—C3—H3108.9 (14)C13—C14—C15118.62 (19)
C5—C3—H3107.1 (14)C13—C14—H14121.8 (14)
C2—C3—H3106.6 (15)C15—C14—H14119.6 (14)
C3—C4—H4A114.4 (17)C14—C15—C10120.82 (17)
C3—C4—H4B100 (2)C14—C15—C16130.61 (18)
H4A—C4—H4B111 (3)C10—C15—C16108.56 (15)
C3—C4—H4C115 (2)C17—C16—C21120.53 (18)
H4A—C4—H4C109 (2)C17—C16—C15131.08 (19)
H4B—C4—H4C107 (3)C21—C16—C15108.36 (15)
C3—C5—H5A112 (2)C16—C17—C18118.6 (2)
C3—C5—H5B112.7 (16)C16—C17—H17118.0 (14)
H5A—C5—H5B109 (3)C18—C17—H17123.4 (14)
C3—C5—H5C107 (2)C17—C18—C19120.8 (2)
H5A—C5—H5C104 (3)C17—C18—H18121.1 (16)
H5B—C5—H5C112 (3)C19—C18—H18118.0 (16)
O1—C6—O2124.21 (15)C18—C19—C20120.84 (19)
O1—C6—C1122.02 (15)C18—C19—H19117.2 (17)
O2—C6—C1113.70 (14)C20—C19—H19121.9 (17)
O3—C7—N1125.15 (15)C21—C20—C19118.5 (2)
O3—C7—O4123.98 (14)C21—C20—H20118.9 (15)
N1—C7—O4110.87 (13)C19—C20—H20122.6 (15)
O4—C8—C9110.58 (13)C20—C21—C16120.73 (16)
O4—C8—H8A109.7 (14)C20—C21—C9129.00 (17)
C9—C8—H8A115.2 (14)C16—C21—C9110.22 (14)
O4—C8—H8B104.0 (13)
C7—N1—C1—C6−134.51 (15)C13—C14—C15—C10−0.3 (3)
C7—N1—C1—C2103.99 (16)C13—C14—C15—C16178.99 (18)
N1—C1—C2—C3−70.9 (2)C11—C10—C15—C140.7 (3)
C6—C1—C2—C3165.48 (17)C9—C10—C15—C14−177.72 (16)
C1—C2—C3—C4−69.5 (3)C11—C10—C15—C16−178.72 (16)
C1—C2—C3—C5165.2 (2)C9—C10—C15—C162.82 (18)
N1—C1—C6—O1159.29 (17)C14—C15—C16—C17−0.5 (3)
C2—C1—C6—O1−76.7 (2)C10—C15—C16—C17178.86 (18)
N1—C1—C6—O2−23.6 (2)C14—C15—C16—C21−178.76 (18)
C2—C1—C6—O2100.39 (19)C10—C15—C16—C210.63 (18)
C1—N1—C7—O3−3.6 (2)C21—C16—C17—C18−0.1 (3)
C1—N1—C7—O4177.08 (13)C15—C16—C17—C18−178.11 (18)
C8—O4—C7—O38.3 (2)C16—C17—C18—C190.3 (3)
C8—O4—C7—N1−172.31 (13)C17—C18—C19—C20−0.7 (3)
C7—O4—C8—C993.78 (16)C18—C19—C20—C210.8 (3)
O4—C8—C9—C1060.54 (17)C19—C20—C21—C16−0.5 (3)
O4—C8—C9—C21172.91 (13)C19—C20—C21—C9−177.57 (17)
C21—C9—C10—C11176.89 (18)C17—C16—C21—C200.2 (2)
C8—C9—C10—C11−67.0 (2)C15—C16—C21—C20178.61 (16)
C21—C9—C10—C15−4.84 (17)C17—C16—C21—C9177.72 (15)
C8—C9—C10—C15111.28 (16)C15—C16—C21—C9−3.83 (18)
C15—C10—C11—C12−0.7 (3)C10—C9—C21—C20−177.46 (17)
C9—C10—C11—C12177.40 (17)C8—C9—C21—C2063.8 (2)
C10—C11—C12—C130.3 (3)C10—C9—C21—C165.24 (17)
C11—C12—C13—C140.1 (3)C8—C9—C21—C16−113.45 (15)
C12—C13—C14—C15−0.1 (3)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O2—H2H···O3i0.85 (3)1.82 (3)2.6558 (17)167 (3)
N1—H1N···O1ii0.87 (3)2.24 (3)3.0751 (18)161 (2)
C8—H8A···O1iii0.90 (2)2.51 (2)3.392 (2)166 (2)

Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) x+1, y, z; (iii) −x, y−1/2, −z+1/2.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FL2198).

References

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