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1.  Synthesis and in Vitro Evaluation of BBB Permeability, Tumor Cell Uptake, and Cytotoxicity of a Series of Carboranylporphyrin Conjugates 
Journal of Medicinal Chemistry  2014;57(15):6718-6728.
A series of tri[(p-carboranylmethylthio)tetrafluorophenyl]porphyrin conjugates of linear and branched polyamines, glucose, arginine, tri(ethylene glycol), and Tyr-d-Arg-Phe-β-Ala (YRFA) peptide were synthesized. These conjugates were investigated for their BBB permeability in human hCMEC/D3 brain endothelial cells, and their cytotoxicity and uptake were assessed using human glioma T98G cells. For comparison purposes, a symmetric tetra[(p-carboranylmethylthio)tetrafluorophenyl]porphyrin was also synthesized, and its crystal structure was obtained. All porphyrin conjugates show low dark cytotoxicity (IC50 > 400 μM) and low phototoxicity (IC50 > 100 μM at 1.5 J/cm2) toward T98G cells. All conjugates were efficiently taken up by T98G cells, particularly the cationic polyamine and arginine conjugates, and were localized in multiple cellular organelles, including mitochondria and lysosomes. All compounds showed relatively low in vitro BBB permeability compared with that of lucifer yellow because of their higher molecular weight, hydrophobicity, and tendency for aggregation in solution. Within this series, the branched polyamine and YRFA conjugates showed the highest permeability coefficient, whereas the glucose conjugate showed the lowest permeability coefficient.
PMCID: PMC4136688  PMID: 25029034
2.  A New Series of Complexes Possessing Rare “Tertiary” Sulfonamide Nitrogen-to-Metal Bonds of Normal Length: fac-[Re(CO)3(N(SO2R)dien)]PF6 Complexes with Hydrophilic Sulfonamide Ligands 
Inorganic chemistry  2014;53(2):1144-1155.
Tertiary sulfonamide nitrogen-to-metal bonds of normal length are very rare. We recently discovered such a bond in one class of fac-[Re(CO)3(N(SO2R)(CH2Z)2)]n complexes (Z = 2-pyridyl) with N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). fac-[M(CO)3(N(SO2R)(CH2Z)2)]n agents (M = 186/188Re, 99mTc) could find use as radiopharmaceutical bioconjugates when R is a targeting moiety. However, the planar, electron-withdrawing 2-pyridyl groups of N(SO2R)dpa destabilize the ligand to base and create relatively rigid chelate rings, raising the possibility that the rare M– N(sulfonamide) bond is an artifact of a restricted geometry. Also, the hydrophobic 2-pyridyl groups could cause undesirable accumulation in the liver, limiting future use in radiopharmaceuticals. Our goal is to identify a robust, hydrophilic, and flexible N(CH2Z)2 chelate framework. New C2-symmetric ligands, N(SO2R)(CH2Z)2 with (Z = CH2NH2; R = Me, dmb, or tol), were prepared by treating N(H)dien(Boc)2, a protected diethylenetriamine (N(H)dien) derivative, with methanesulfonyl chloride (MeSO2Cl), 3,5-dimethylbenzenesulfonyl chloride (dmbSO2Cl), and 4-methylbenzenesulfonyl chloride (tolSO2Cl). Treatment of fac-[Re(CO)3(H2O)3]+ with these ligands, designated as N(SO2R)dien, afforded new fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes. Comparing the fac-[Re(CO)3(N(SO2Me)dien)]PF6 and fac-[Re(CO)3(N(SO2Me)dpa)]PF6 complexes, we find that the ReI–N(sulfonamide) bonds are normal in length and statistically identical and that the methyl 13C NMR signal has an unusually upfield shift compared to that in the free ligand. We attribute this unusual upfield shift to the fact that the sulfonamide N undergoes an sp2-to-sp3 rehybridization upon coordination to ReI in both complexes. Thus, the sulfonamide N of N(SO2R)dien ligands is a good donor, even though the chelate rings are conformationally flexible. Addition of the strongly basic and potentially monodentate ligand, 4-dimethylaminopyridine, did not affect the fac-[Re(CO)3(N(SO2tol)dien)]PF6 complex, even after several weeks. This complex is also stable to heat in aqueous solution. These results indicate that N(SO2R)dien ligands form fac-[Re(CO)3(N(SO2R)dien)]PF6 complexes sufficiently robust to be utilized for radiopharmaceutical development.
PMCID: PMC4465231  PMID: 24400928
3.  Formation of a Metal-to-Nitrogen Bond of Normal Length by a Neutral Sufonamide Group within a Tridentate Ligand. A New Approach to Radiopharmaceutical Bioconjugation 
Inorganic chemistry  2013;52(5):2412-2421.
We demonstrate that a tertiary sulfonamide group, N(SO2R)R′2, can re-hybridize to form a M–N bond of normal length even when the group is in a linear tridentate ligand, such as in the new tridentate N(SO2R)dpa ligands derived from di-(2-picolyl)amine (N(H)dpa). N(SO2R)dpa ligands were used to prepare fac-[Re(CO)3(N(SO2R)dpa)](PF6 or BF4) complexes. Structural characterization of the new complexes established that the tertiary sulfonamide nitrogen atom binds to Re with concomitant sp2-to-sp3 re-hybridization, facilitating facial coordination. The new fac-[Re(CO)3(N(SO2R)dpa)]X structures provide the only examples for any metal with the sulfonamide as part of a noncyclic linear tridentate ligand and with a normal metal-to-nitrogen(tertiary sulfonamide) bond length. Rare previous examples of such normal M–N bonds have been found only in more constrained situations, such as with tripodal tetradentate ligands. Our long-term objectives for the new tridentate N(SO2R)dpa ligands are to develop the fundamental chemistry relevant to the eventual use of the fac-[MI(CO)3]+ core (M = 99mTc, 186/188Re) in imaging and therapy. The sulfonamide group uniquely contributes to two of our goals: expanding ways to conjugate the fac-[MI(CO)3]+ core to biological molecules and also developing new symmetrical tridentate ligands that can coordinate facially to this core. Tests of our conjugation method, conducted by linking the fac-[ReI(CO)3]+ core to a new tetraarylporphyrin (T(N(SO2C6H4)dpa)P) as well as to a dansyl (5-(dimethylamino)naphthalene-1-sulfonyl) group, demonstrate that large molecular fragments can be tethered via a coordinated tertiary sulfonamide linkage to this core.
PMCID: PMC4465213  PMID: 23421481
4.  Discovery and Structure–Activity Relationship of Novel 2,3-Dihydrobenzofuran-7-carboxamide and 2,3-Dihydrobenzofuran-3(2H)-one-7-carboxamide Derivatives as Poly(ADP-ribose)polymerase-1 Inhibitors 
Journal of Medicinal Chemistry  2014;57(13):5579-5601.
Novel substituted 2,3-dihydrobenzofuran-7-carboxamide (DHBF-7-carboxamide) and 2,3-dihydrobenzofuran-3(2H)-one-7-carboxamide (DHBF-3-one-7-carboxamide) derivatives were synthesized and evaluated as inhibitors of poly(ADP-ribose)polymerase-1 (PARP-1). A structure-based design strategy resulted in lead compound 3 (DHBF-7-carboxamide; IC50 = 9.45 μM). To facilitate synthetically feasible derivatives, an alternative core was designed, DHBF-3-one-7-carboxamide (36, IC50 = 16.2 μM). The electrophilic 2-position of this scaffold was accessible for extended modifications. Substituted benzylidene derivatives at the 2-position were found to be the most potent, with 3′,4′-dihydroxybenzylidene 58 (IC50 = 0.531 μM) showing a 30-fold improvement in potency. Various heterocycles attached at the 4′-hydroxyl/4′-amino of the benzylidene moiety resulted in significant improvement in inhibition of PARP-1 activity (e.g., compounds 66–68, 70, 72, and 73; IC50 values from 0.718 to 0.079 μM). Compound 66 showed selective cytotoxicity in BRCA2-deficient DT40 cells. Crystal structures of three inhibitors (compounds (−)-13c, 59, and 65) bound to a multidomain PARP-1 structure were obtained, providing insights into further development of these inhibitors.
PMCID: PMC4094269  PMID: 24922587
5.  Synthesis and Transformations of 5-Chloro-2,2′-Dipyrrins and Their Boron Complexes, 8-Chloro-BODIPYs** 
Symmetric dipyrrylketones 1a,b were synthesized in two steps from the corresponding α-free pyrroles, by reaction with thiophosgene followed by oxidative hydrolysis under basic conditions. The dipyrrylketones produced the corresponding 5-chloro-dipyrrinium salts or 5-ethoxy-dipyrrins on reaction with phosgene or Meerwein’s salt, respectively. Boron complexation of the dipyrrins afforded the corresponding 8-functionalized BODIPYs (borondipyrromethenes) in high yields. The 5-chloro-dipyrrinium salts reacted with methoxide or ethoxide ions to produce monopyrrole esters, presumably via a 5,5-dialkoxy-dipyrromethane intermediate. In contrast, 8-chloro-BODIPYs underwent a variety of nucleophilic substitutions of the chloro group in the presence of alkoxide ions, Grignard reagents, and thiols. In the presence of excess alkoxide or Grignard reagent, at room temperature or above, substitution at the boron center also occurred. The 8-chloro-BODIPY was a particularly useful reagent for the preparation of 8-aryl-, 8-alkyl-, and 8-vinyl-substituted BODIPYs in very high yields, using Pd0-catalyzed Stille cross-coupling reactions. The X-ray structures of eleven BODIPYs and two pyrroles are presented, and the spectroscopic properties of the synthesized BODIPYs are discussed.
PMCID: PMC4012389  PMID: 24616111
bodipy; dipyrrin; dipyrrylketone; fluorescence
6.  Phenyl Derivative of Iron 5,10,15-Tritolylcorrole 
Inorganic Chemistry  2014;53(8):4215-4227.
The phenyl–iron complex of 5,10,15-tritolylcorrole was prepared by reaction of the starting chloro–iron complex with phenylmagnesium bromide in dichloromethane. The organometallic complex was fully characterized by a combination of spectroscopic methods, X-ray crystallography, and density functional theory (DFT) calculations. All of these techniques support the description of the electronic structure of this phenyl–iron derivative as a low-spin iron(IV) coordinated to a closed-shell corrolate trianion and to a phenyl monoanion. Complete assignments of the 1H and 13C NMR spectra of the phenyl–iron derivative and the starting chloro–iron complex were performed on the basis of the NMR spectra of the regioselectively β-substituted bromo derivatives and the DFT calculations.
The preparation of complex 1 fills a gap in the series of triarylcorrole iron derivatives. The spectroscopic and theoretical characterization of this complex indicates that it can be described as an Fe(IV) derivative, with a nonoxidized corrole species, acting as a trianionic ligand. However also in this case significant spin density is present on the corrole ring, as predicted by DFT calculations and confirmed by the 1H NMR isotropic shifts.
PMCID: PMC4002138  PMID: 24697623
7.  Colourimetric and fluorescent detection of oxalate in water by a new macrocycle-based dinuclear nickel complex: a remarkable red shift of the fluorescence band† 
A new macrocycle-based dinuclear nickel chemosensor selectively binds oxalate anions both in solution and the solid state, displaying a remarkable red shift of the fluorescence band with a visible colour change in water at physiological pH in the presence of an external dye.
PMCID: PMC3976989  PMID: 24419223
8.  Scalable Preparation and Differential Pharmacologic and Toxicologic Profiles of Primaquine Enantiomers 
Hematotoxicity in individuals genetically deficient in glucose-6-phosphate dehydrogenase (G6PD) activity is the major limitation of primaquine (PQ), the only antimalarial drug in clinical use for treatment of relapsing Plasmodium vivax malaria. PQ is currently clinically used in its racemic form. A scalable procedure was developed to resolve racemic PQ, thus providing pure enantiomers for the first time for detailed preclinical evaluation and potentially for clinical use. These enantiomers were compared for antiparasitic activity using several mouse models and also for general and hematological toxicities in mice and dogs. (+)-(S)-PQ showed better suppressive and causal prophylactic activity than (−)-(R)-PQ in mice infected with Plasmodium berghei. Similarly, (+)-(S)-PQ was a more potent suppressive agent than (−)-(R)-PQ in a mouse model of Pneumocystis carinii pneumonia. However, at higher doses, (+)-(S)-PQ also showed more systemic toxicity for mice. In beagle dogs, (+)-(S)-PQ caused more methemoglobinemia and was toxic at 5 mg/kg of body weight/day given orally for 3 days, while (−)-(R)-PQ was well tolerated. In a novel mouse model of hemolytic anemia associated with human G6PD deficiency, it was also demonstrated that (−)-(R)-PQ was less hemolytic than (+)-(S)-PQ for the G6PD-deficient human red cells engrafted in the NOD-SCID mice. All these data suggest that while (+)-(S)-PQ shows greater potency in terms of antiparasitic efficacy in rodents, it is also more hematotoxic than (−)-(R)-PQ in mice and dogs. Activity and toxicity differences of PQ enantiomers in different species can be attributed to their different pharmacokinetic and metabolic profiles. Taken together, these studies suggest that (−)-(R)-PQ may have a better safety margin than the racemate in human.
PMCID: PMC4136050  PMID: 24913163
9.  Absorption of atmospheric CO2 as carbonate inside the molecular cavity of a new tripodal hexaurea receptor 
Organic letters  2013;16(2):366-369.
A new hexaurea receptor has been synthesized, which absorbs atmospheric CO2 to produce an air-stable solid carbonate complex under normal conditions. Structural analysis of the carbonate complex with this receptor suggests that the carbonate is fully encapsulated within its highly organized intramolecular cavity via twelve strong NH···O bonds in the range of 2.703(3) – 2.989(3) Å from six urea units, with each anionic oxygen coordinated via four NH···O bonds with two urea groups.
PMCID: PMC3976990  PMID: 24350563
10.  Absolute configuration of naturally occurring glabridin 
Glabridin is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration.
The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-di­hydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH–H2O mixture (95:5 v/v) to yield colorless crystals containing one mol­ecule per asymmetric unit (Z′ = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantio­purity of any isolated or synthetic glabridin sample.
PMCID: PMC4028893  PMID: 24192160
crystal structure; absolute configuration; glabridin; natural compounds
11.  β-Pyrazino-fused tetrarylporphyrins 
Dyes and pigments : an international journal  2013;99(1):10.1016/j.dyepig.2013.04.024.
A novel method for the preparation of β-fused porphyrin dyads was developed that exploits a one-pot reaction of 2,3-diaminoporphyrins with diethyl oxalate. This approach provides good yields of the zinc β-fused dyad and the corresponding free-base, opening the way for preparation of several metal derivatives to permit modulation of optoelectronic characteristics for commercial applications.
PMCID: PMC3863362  PMID: 24347747
β-fused-porphyrin; Dietyl oxalate; α-dione porphyrin; 2,3-Diaminoporphyrin; DSSC; Porphyrin dyad electrochemistry
12.  Asteropsin A: An unusual cystine-crosslinked peptide from porifera enhances neuronal Ca2+ influx 
Biochimica et biophysica acta  2013;1830(3):2591-2599.
Herein we report the discovery of a cystine-crosslinked peptide from Porifera along with high-quality spatial details accompanied by the description of its unique effect on neuronal calcium influx.
Asteropsin A (ASPA) was isolated from the marine sponge Asteropus sp., and its structure was independently determined using X-ray crystallography (0.87 Å) and solution NMR spectroscopy.
An N-terminal pyroglutamate modification, uncommon cis proline conformations, and absence of basic residues helped distinguish ASPA from other cystine-crosslinked knot peptides. ASPA enhanced Ca2+ influx in murine cerebrocortical neuron cells following the addition of the Na+ channel activator veratridine but did not modify the oscillation frequency or amplitude of neuronal Ca2+ currents alone. Allosterism at neurotoxin site 2 was not observed, suggesting an alternative to the known Na+ channel interaction.
Together with a distinct biological activity, the origin of ASPA suggests a new subclass of cystine-rich knot peptides associated with Porifera.
General significance
The discovery of ASPA represents a distinctive addition to an emerging subclass of cystine-crosslinked knot peptides from Porifera.
PMCID: PMC4137556  PMID: 23201194
Porifera; Ion channelopathy; Natural product; Bioactive peptide; X-ray crystallography; NMR spectroscopy
13.  Spectroscopic, computational modeling and cytotoxicity of a series of meso-phenyl and meso-thienyl-BODIPYs 
Bioorganic & medicinal chemistry  2013;21(18):5770-5781.
A series of twenty-two BODIPY compounds were synthesized, containing various meso-phenyl and meso-thienyl groups, and their spectroscopic and structural properties were investigated using both experimental and computational methods. Further functionalization of the BODIPY framework via iodination at the 2,6-pyrrolic positions was explored in order to determine the effect of these heavy atoms on the photophysical and cytotoxicity of the meso-aryl-BODIPYs. BODIPYs bearing meso-thienyl substituents showed the largest red-shifted absorptions and emissions and reduced fluorescence quantum yields. The phototoxicity of the BODIPYs in human carcinoma HEp2 cells depends on both the presence of iodines and the nature of the meso-aryl groups. Six of the eleven 2,6-diiodo-BODIPYs investigated showed at least a sevenfold enhancement in phototoxicity (IC50 = 3.5–28 μM at 1.5 J/cm2) compared with the non-iodinated BODIPYs, while the others showed no cytotoxicity, while their singlet oxygen quantum yields ranged from 0.02 to 0.76. Among the series investigated, BODIPYs 2a and 4a bearing electron-donating meso-dimethoxyphenyl substituents showed the highest phototoxicity and dark/phototoxicity ratio, and are therefore the most promising for application in PDT.
PMCID: PMC4133122  PMID: 23928070
BODIPY; PDT; Fluorescence; Phototoxicity; Cellular uptake
14.  Labdane Diterpenoids from Leonotis leonurus 
Phytochemistry  2012;91:229-235.
Three known (leoleorins A-C) and eight new (leoleorins D-J and 16-epi-leoleorin F) labdane diterpenoids, were isolated from leaves of Leonotis leonurus. The absolute configurations of leoleorins A and D were established by X-ray crystallographic analyses. In competitive binding assay all isolated compounds showed inhibition in excess of 50% at various CNS receptors. Leoleorin C showed moderate binding affinity (Ki = 2.9 μM) for the Sigma 1 receptor.
PMCID: PMC3390464  PMID: 22445074
Leonotis leonurus; Lamiaceae; Psychoactive plant; Labdane diterpenoids; Leoleorins A-J; X-ray diffraction; G-protein-coupled receptors
15.  New Monodentate Amidine Superbasic Ligands with a Single Configuration in fac-[Re(CO)3(5,5′- or 6,6′-Me2bipyridine)(amidine)]BF4 Complexes 
Inorganic chemistry  2012;51(13):7271-7283.
Treatment of two precursors, fac-[Re(CO)3(L)(CH3CN)]BF4 [L = 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me2bipy) (1) and 6,6′-dimethyl-2,2′-bipyridine (6,6′-Me2bipy) (2)], with five C2-symmetrical saturated heterocyclic amines yielded ten new amidine complexes, fac-[Re(CO)3(L)(HNC(CH3)N(CH2CH2)2Y)]BF4 [Y = CH2, (CH2)2, (CH2)3, NH or O]. All ten complexes possess the novel feature of having only one isomer (amidine E configuration), as established by crystallographic and 1H NMR spectroscopic methods. We are confident that NMR signals of the other possible isomer (amidine Z configuration) would have been detected, if it were present. Isomers are readily detected in closely related amidine complexes because the double-bond character of the amidine C–N3 bond (N3 is bound to Re) leads to slow E to Z isomer interchange. The new fac-[Re(CO)3(L)(HNC(CH3)N(CH2CH2)2Y)]BF4 complexes have C–N3 bonds with essentially identical double-bond character. However, the reason that the Z isomer is so unstable as to be undetectable in the new complexes is undoubtedly because of unfavorable clashes between the equatorial ligands and the bulky N(CH2CH2)2Y ring moiety of the axial amidine ligand. The amidine formation reactions in acetonitrile (25 °C) proceeded more easily with 2 than with 1, indicating that the distortion in 6,6′-Me2bipy resulting from the proximity of the methyl substituents to the inner coordination sphere enhanced the reactivity of the coordinated CH3CN. Reaction times for 1 and 2 exhibited a similar dependence on the basicity and ring size of the heterocyclic amine reactants. Moreover, when the product of the reaction of 1 with piperidine, fac-[Re(CO)3(5,5′-Me2bipy)(HNC(CH3)N(CH2CH2)2CH2)]BF4, was challenged in acetonitrile-d3 or CDCl3 with a fivefold excess of the strong 4-dimethylaminopyridine ligand, there was no evidence for replacement of the amidine ligand after two months, thus establishing that the piperidinylamidine ligand is a robust ligand. This chemistry offers promise as a suitable means for preparing isomerically pure conjugated fac-[99mTc(CO)3L]n+/− imaging agents, including conjugates with known bioactive heterocyclic amines.
PMCID: PMC4059189  PMID: 22691073
16.  Hexa-μ-acetato-1:2κ4 O,O′;1:2κ2 O:O;2:3κ4 O,O′;2:3κ2 O:O-bis­(4,4′-dimethyl-2,2′-bi­pyridine)-1κ2 N,N′;3κ2 N,N′-2-calcium-1,3-dizinc 
In the centrosymmetric trinuclear ZnII⋯CaII⋯ZnII title complex, [CaZn2(CH3COO)6(C12H12N2)2], the CaII ion lies on an inversion centre and is octa­hedrally coordinated by six acetate O atoms. The ZnII ion is coordinated by two N atoms from a bidentate di­methyl­bipyridine ligand and three O atoms from acetate ligands bridging to the CaII ion, leading to a distorted square-pyramidal coordination sphere. The Zn⋯Ca distance is 3.4668 (5) Å.
PMCID: PMC3884985  PMID: 24454160
17.  Copper β-trinitrocorrolates 
Journal of porphyrins and phthalocyanines  2013;17(6-7):10.1142/S1088424613500120.
The β-nitration reaction carried out on the corrole macrocycle has been shown to be extremely regioselective, although the reduced symmetry of the macrocycle could potentially lead to a huge number of possible regioisomers. We recently reported that the careful use of AgNO2/NaNO2 as a nitrating system enabled the achievement in good yields of mono- and dinitro-derivatives on both corrole free base and its copper complex, proving to be an efficient and cost-effective method. In this work, we present a detailed study of the scope of this method using TtBuCorrH3 as a model corrole. A further increase of the oxidant pushes the nitration up to the functionalization of three β-pyrrolic positions, although concomitant decomposition of the macrocycle is also observed. The application of the proven nitration method with a five-fold excess of both silver and sodium nitrites with respect to corrole, afforded the 2,3,17-(NO2)3-TtBuPCorrCu as the main product, in 25% yield, together with traces of another compound identified by X-ray crystallographic analysis as the 3,8,17-(NO2)3-TtBuPCorrCu isomer. In light of these recent results, we also reinvestigated the characterization of the nitration products obtained from bis-substitution reactions, allowing among others the identification of the copper 3,8-(NO2)2 corrolate.
PMCID: PMC3811046  PMID: 24179331
corrole; β-functionalization; nitration; AgNO2
18.  1,1′,4,5-Tetra­hydro­tri­spiro­[1,3,2-di­aza­phosphole-2,2′-[1,3,5,2,4,6]tri­aza­triphosphinine-4′,6′′-dibenzo[d,f][1,3,2]dioxaphosphepine-6′,6′′′-dibenzo[d,f][1,3,2]dioxaphosphepine] acetone monosolvate 
The title compound, C26H22N5O4P3·C3H6O, has been achieved in a two-step synthesis that does not require chromatography. This mol­ecule contains a seven-membered spiro­cyclic ring at two P-atom positions and a five-membered ring containing new P—N bonds at the other P-atom position. Endocyclic torsion angles about the central biphenyl C—C bonds are −41.5 (3) and −44.4 (3)°, and P—N bonds of the central P3N3 ring are within the range 1.5665 (17)–1.6171 (17) Å, while the P—O distances are in the range 1.5940 (14)–1.6041 (14) Å. One N—H group makes an inter­molecular N—H⋯N hydrogen bond, forming centrosymmetric dimers, while the other N—H group makes an N—H⋯O hydrogen bond to the acetone solvent mol­ecule. The crystal was a two-component non-merohedral twin with ratio 0.811/0.189.
PMCID: PMC3884451  PMID: 24427109
19.  Tris(4-formyl­phen­yl)phosphane oxide tetra­hydro­furan hemisolvate 
The title compound, C21H15O4P·0.5C4H8O, contains an ordered phosphane oxide in a general position and a tetra­hydro­furan solvent mol­ecule disordered about a twofold axis. All three aldehyde substituents are nearly coplanar with their attached benzene rings, with C—C—C—O torsion angles in the range 1.64 (17)–4.24 (19)°. All three have different conformations with respect to the P=O group, one syn, one anti, and one gauche. Two of the aldehyde substituents form inter­molecular C—H⋯O contacts.
PMCID: PMC3793837  PMID: 24109424
20.  Synthesis, characterization, and preliminary in vitro studies of vanadium(IV) complexes with a Schiff base and thiosemicarbazones as mixed-ligands 
[VO(Sal-L-tryp)(H2O)] 1 (where sal-L-tryp = N-salicylidene-L-tryptophanate) was used as a precursor to produce the novel complexes, [VO(Sal-L-tryp)(MeATSC)].1.5C2H5OH 2 (where MeATSC = 9-Anthraldehyde-N(4)-methylthiosemicarbazone), [VO(Sal-L-tryp)(N-Ethhymethohcarbthio)].H2O 3 (where N-Ethhymethohcarbthio = (E)-N-ethyl-2-(4-hydroxy-3-methoxybenzylidene)hydrazinecarbothioamide), and [VO(Sal-L-tryp)(acetylethTSC)].C2H5OH 4 (where acetylethTSC = (E)-N-ethyl-2-(1-(thiazol-2-yl)ethylidene)hydrazinecarbothioamide), by reaction with the respective thiosemicarbazone. The chemical and structural properties of these ligands and complexes were characterised by elemental analysis, ESI MS, FT-IR, UV-visible, ESR, 1H and 13C NMR spectroscopy, and X-ray crystallography. DMSO and DMSO-d6 solutions of compounds 1-4 were oxidised in air to produce vanadium(V) species which were verified by ESI MS and 51V NMR spectroscopy. Anti-cancer properties of compounds 2-4 were examined with three colon cancer cell lines, HTC-116, Caco-2, and HT-29, and also with non-cancerous colonic myofibroblasts, CCD18-Co. Compounds 2-3 exhibited less inhibitory effects in the CCD-18Co cells, indicating a possible cytotoxic selectivity towards colon cancer cells. In general, those compounds which exhibited anti-proliferative activity on cancer cells, but did not affect non-cancerous cells, may have a potential in chemotherapy.
PMCID: PMC3725831  PMID: 23904789
vanadium(IV); vanadium(V); 51V NMR; ESR spectroscopy; thiosemicarbazone; colorectal cancer
21.  Field effects induce bathochromic shifts in xanthene dyes 
Journal of the American Chemical Society  2012;134(25):10502-10508.
There is ongoing interest in near infrared (NIR) absorbing and emitting dyes for a variety of biomedical and materials applications. Simple and efficient synthetic procedures enable the judicious tuning of through-space polar (field) effects as well as low barrier hydrogen bonding to modulate the HOMO-LUMO gap in xanthene dyes. This affords unique NIR-absorbing xanthene chromophores.
PMCID: PMC3384756  PMID: 22642754
xanthenes; near-infrared; large Stokes shift
22.  β-Nitro-5,10,15-tritolylcorroles 
Inorganic Chemistry  2012;51(12):6928-6942.
Functionalization of the β-pyrrolic positions of the corrole macrocycle with –NO2 groups is limited at present to metallocorrolates due to of the instability exhibited by corrole free bases under oxidizing conditions. A careful choice of the oxidant can limit the transformation of corroles into decomposition products or isocorrole species, preserving the corrole aromaticity, and thus allowing the insertion of nitro groups onto the corrole framework. Here we report results obtained by reacting 5,10,15-tritolylcorrole (TTCorrH3) with the AgNO2/NaNO2 system, to give mono- and di-nitrocorrole derivatives when stoichiometry is carefully controlled. Reactions were found to be regioselective, affording the 3-NO2TTCorrH3 and 3,17-(NO2)2TTCorrH3 isomers as the main products in the case of mono- and di-substitution, in 53 and 20% yields, respectively. In both cases, traces of other mono- and di-substituted isomers were detected, which were structurally characterized by X-ray crystallography. The influence of the β-nitro substituents on the corrole properties is studied in detail by UV-visible, electrochemical, and spectroelectrochemical characterization of these functionalized corroles. Density Functional Theory (DFT) and time-dependent DFT (TDDFT) calculations of the ground and excited state properties of these β-nitrocorrole derivatives also afforded significant information, closely matching the experimental observations. It is found that the β-NO2 substituents conjugate with the π-aromatic system of the macrocycle, which initiates significant changes in both the spectroscopic and redox properties of the so functionalized corroles. This effect is more pronounced when the nitro group is introduced at the 2-position, because in this case the conjugation is, for steric reasons, more efficient than in the 3-nitro isomer.
PMCID: PMC3381796  PMID: 22668242
23.  Bis-spirolabdane Diterpenoids from Leonotis nepetaefolia 
Journal of Natural Products  2012;75(4):728-734.
Ten new bis-spirolabdane diterpenoids, leonepetaefolins A–E (1, 3, 5, 7, 9) and 15-epi-leonepetaefolins A-E (2, 4, 6, 8, 10), together with eight known labdane diterpenoids (11–18) as well as two known flavonoids apigenin and cirsiliol, were isolated from the leaves of Leonotis nepetaefolia. The structures of the new compounds were determined on the basis of 1D-and 2D-NMR experiments including 1H, 13C, DEPT, 1H-1H COSY, HSQC, HMBC, and NOESY. The absolute configuration of an epimeric mixture of 1 and 2 was determined by X-ray crystallographic analysis. The compounds isolated were evaluated for their binding propensity in several CNS G protein-coupled receptor assays in vitro.
PMCID: PMC3338874  PMID: 22475308
24.  Iodido{4-phenyl-1-[1-(1,3-thia­zol-2-yl-κN)ethyl­idene]thio­semicarbazidato-κ2 N′,S}{4-phenyl-1-[1-(1,3-thia­zol-2-yl)ethyl­idene]thio­semicarbazide-κS}cadmium(II) 
In the title complex, [Cd(C12H11N4S2)I(C12H12N4S2)], the CdII ion is penta­coordinated by two thio­semicarbazone ligands (one neutral and the other anionic) and one iodide ion in a distorted square pyramidal (τ = 0.35) geometry. The central ion is coordinated by the thia­zole N atom, the thio­ureido N and the S atom of the deprotonated thio­semicarbazone ligand. The other ligand is linked with the central ion through the C=S group. The deprotonated ligand intra­molecularly hydrogen bonds to the thia­zole ring N atom, while the ligand forms an inter­molecular hydrogen bond to the thiol­ate S atom of the second ligand. The deprotonation of the tridentate ligand and its coordination to the CdII ion via the S atom strikingly affects the C—S bond lengths. The C—S bond lengths in the neutral and deprotonated ligands in the metal complex are 1.709 (3) and 1.748 (2) Å, respectively, whereas it is 1.671 (3) Å in the free ligand. In the metal complex, the Cd—S distances are 2.6449 (6) and 2.5510 (6) Å. The Cd—I bond length is 2.7860 (2) Å.
PMCID: PMC3647796  PMID: 23723762
25.  (Z)-1-(2-Hy­droxy­eth­yl)-4-(2-meth­oxy­benzyl­idene)-2-methyl-1H-imidazol-5(4H)-one 
In the title compound, C14H16N2O3, an analog of the chromophore in green fluorescent protein, the meth­oxy­phenyl substituent and the imidazole N adopt a Z conformation with respect to the C=C bond. Aside from the hy­droxy­ethyl group, the mol­ecule is approximately planar, with the five- and six-membered ring planes forming a dihedral angle of 9.3 (1)°. An intra­molecular C—H⋯N contact occurs. In the crystal, O—H⋯N hydrogen bonds link the mol­ecules, forming chains along the b-axis direction. C—H⋯O hydrogen bonds are also observed.
PMCID: PMC3629644  PMID: 23634131

Results 1-25 (149)