Letters in Organic Chemistry - Volume 8, Issue 10, 2011

A practical synthetic route of DOPA derivative 2, which should be useful for direct biosynthetic production of potent antitumor natural products, saframycins and ecteinascidin 743 was established. The developed strategy features i) easy-to-handle reactions without special care upon both dryness and inert atmopsphere, and ii) the facile HPLC-free purification of 2 via recrystallization enabling scalable synthesis of 2.

The carbonyl compounds and the aryl halides are efficiently reduced by Ni-Al alloy powder, in aqueous alkali medium, with or without organic solvents. The relative reactivities in a series of structurally selected reducible compounds showed a sequence of reactivity in agreement with the mechanism involving a direct electron transfer from aluminum to the organic phase. In some cases an important change in reactivity with respect to conversion of the reducing reagent was notified. Most probably this complicated variability is the result of the changes in composition and morphology of the reacting Ni-Al alloy.

In this study, the lipase-catalyzed kinetic resolution (Novozyme 435) was employed to prepare chiral allylic alcohols and acetates with terminal double bonds in enantiomeric excesses ranging from 94 to > 99 %.

1,2,3-triazoles were synthesized using several alkynes and azides as starting materials in the presence of glucose and catalytic amounts of Fehling reagent. This process is carried out under ambient pressure and temperature with good yields

An environmentally rapid and benign protocol for the synthesis of 4-aryl-1,4-dihydropyridines compounds using VB1 as a catalyst under microwave irradiation and solvent-free conditions has been achieved. The procedure is operationally simple, giving good to high product yield.

Direct interaction of indolylzinc chloride with 2,5-dichloro-3,4-dinitrothiophene (4) produced 2,5-bis(indol-3- yl)-3,4-dinitrothiophene (5) together with 3-(5-chloro-3,4-dinitrothien-2-yl)indole (6). Interaction of the latter compound with 1-methylpiperazine gave 3-[4,5-di(4-methylpiperazin-1-yl)-3-nitrothien-2-yl]indole (7), as the expected SN-Ar (addition-elimination) di-substitution product, together with 3-[5-(4-methylpiperazin-1-yl)-3-nitrothien-2-yl]indole (8), a mono-substituted product. The formation of 8 probably proceeds via an anomalous pathway, related to cine-substitution, with departure of the nitro group at C-4'. Compound 4 underwent SN-Ar substitution reaction with 1-methylpiperazine to give the respective 2,5-di-(4-methylpiperazin-1-yl)-2,4-dinitrothiophene (9).

Three-component condensation of substituted acetophenones, aromatic aldehydes, and ammonium acetate catalyzed by silver(I) nitrate adsorbed on silica gel nanoparticles (AgNO3-nano SiO2) has been accomplished for the synthesis of a series of 2,4,6-triaryl pyridines in good to excellent yields under solvent-free conditions.

European Pharmacopeia mentions about nine potential impurities in Granisetron hydrochloride. These impurities need to be controlled in the API as described in the Pharmacopeia. Elegant syntheses of four potential impurities in Granisetron hydrochloride are disclosed.

Two new substituted dithieno[2,3-b:3',2'-d]siloles, 7,7-diphenyl-2,5-bis(trimethylsilyl) dithieno[2,3-b:3',2'- d]silole (1) and 7,7-diphenyl-2,5-dichloro-dithieno[2,3-b:3',2'-d]silole (2) were synthesized in 79.4% and 31.6% yields, respectively via the cross-coupling of 1,4-dilithiobutadienes with dichlorodiphenylsilane. An unexpected tetrachlorosubstituted 10-membered silicon-bridged thiophene-based cyclophane (3) was obtained in a high yield as 46.9% when the cross-coupling of 1,4-dilithiobutadiene reacted with dichlorodimethylsilane. In addition, the crystal structures of title compounds are described.

A simple and efficient synthetic approach to 1,4-disubstituted piperazine-2,5-diones was developed. A series of symmetrical 1,4-disubstituted piperazine-2,5-diones was prepared from chloroacetamides using potassium iodide catalysis in acetone/water. The structures of two products were confirmed by single crystal X-ray diffraction analysis.

A series of optically active β-aryloxy alcohols and β-arylthiol alcohols were synthesized directly by asymmetric transfer hydrogenation of the corresponding β-carbonyl ethers or β-carbonyl sulfides in excellent yields (up to 99%) and excellent enantioselectivity (up to 100% ee) under mild reaction conditions.

A straightforward, simple and efficient method is described for the synthesis of pyrazolo[1,2-a][1,2,4]triazole derivates via one-pot three-component reaction between isocyanides, dialkyl acetylenedicarboxylate and 4-phenyl urazole (as a NH-acid) in acetone without using any catalyst at ambient temperature. This method offers several advantages such as high yield of products, easy work-up procedure and mild reaction conditions.

A highly sensitive fluorescent probe (3) for selective detection of mercury based on an azobenzene derivative with 1,3,4-triazole units has been designed, synthesized, and examined for their cation recognition abilities toward various cations by UV-vis, fluorescence. The fluorescent probe (3) exhibits a highly selective response of fluorescence enhancement toward mercury in DMF aqueous media (DMF: H2O, v/v=1:1).

This study demonstrates a methodology for evaluating the theoretical antimalarial potential of 18 phenazine derivatives, some of which have no known biological activities. Semi-empirical, density functional and statistical methods for analytical data treatment were used to establish a quantitative structure-activity relationship (QSAR). A set of 16 descriptors were obtained. Theoretical tools regarding inferential statistics were used to analyze and interpret the information necessary for the application of a multivariate analysis. We classified four types of phenazines into distinct clusters taking into account including planarity, ring-attached substituents, geometric arrangement and conjugation effects, energy maps as well as frontier orbitals energies. The experimental data and crystallochemical analysis obtained in the present study were able to substantiate the chemo-theoretical analysis. Our classifications agree well with experimental evidence regarding compounds that have already been studied. it would also be desirable to conduct new experimental studies in order to further evaluate the predicting capability of our calculations.