A stereoselective total synthesis of (+)-α-herbertenol

A stereoselective total synthesis of (+)-α-herbertenol starting from the allyl alcohol 12, readily available in three steps from the monoterpene (R)-limonene, is described. Claisen rearrangement of the aryl allyl ether 10 and concomitant cyclisation furnished a 5:3 mixture of the tricyclic compounds 13 and 14. Degradation of the isopropenyl group followed by cleavage of the central ring and functional group manipulation transformed 13 into (+)-α-herbertenol (1b).     

A Rapid Densitometric Method for the Quantification of Luteolin in Medicinal Plants Using HPTLC

Luteolin, a flavonoid, is reported to occur widely in many medicinal plants. It has been shown to have important biological activities. We report sensitive HPTLC method for the quantification of luteolin from plant material. The method was validated for precision, repeatability and accuracy. The method was found to be precise with RSDs for intraday in the range of 0.77–1.29% and inter–day in the range of 1.02–2.08%. Instrumental precision and repeatability of the method were found to be 0.39 and 0.57 (%CV). Accuracy of the method was checked by recovery study conducted at two different levels and the average percentage recovery was found to be 100.92%. The method was used for quantification of luteolin in three important herbal drugs viz. fruit of Cuminum cyminum, whole plant of Bacopa monnieri, flower of Achillea millefolium. The proposed HPTLC method for the quantification of luteolin was found to be simple, precise, specific, sensitive and accurate and can be used for quality control of raw materials.Revised: 1 October 2003 and 18 February 2004     

Kinetics of 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate/n-alkane organogel formation and its influence on the fibrillar networks

The kinetics and mode of nucleation and growth of fibers by 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate (CNC), a low-molecular-mass organogelator (LMOG), in n-octane and n-dodecane have been investigated as their sols were transformed isothermally to organogels. The kinetics has been followed in detail by circular dichroism, fluorescence, small-angle neutron scattering, and rheological methods. When treated according to Avrami theory, kinetic data from the four methods are self-consistent and describe a gelation process involving one-dimensional growth and "instantaneous nucleation". As expected from this growth model, polarized optical micrographs of the self-assembled fibrillar networks (SAFINs) show fibrous aggregates. However, their size and appearance change abruptly from spherulitic to rodlike as temperature is increased. This morphological change is attended by corresponding excursions in static and kinetic CD, fluorescence and rheological data. Furthermore, the rheological measurements reveal an unusual linear increase in viscoelastic moduli in the initial stages of self-assembly. Each of the methods employed becomes sensitive to changes of the system at different stages of the transformation from single molecules of the LMOG to their eventual SAFINs. This study also provides a methodology for investigating aggregation phenomena of some other self-assembling systems, including those of biological and physiological importance.     

Zeylanone and Isozeylanone,two novel quinones from Plumbago Zeylanica

Zeylanone and isozeylanone have been shown to be novel dimers of plumbagin (2-methyl-5-hydroxy-1,4-naphthaquinone). A probable mode of their formation in vivo from plumbagin (1) and its hydroquinone (3) has been postulated (Scheme 1). Benzene induced solvent shifts of the aromatic protons of zeylanone have been discussed.     

Synthesis of conformationally constrained cyclic peptides using an intramolecular sonogashira coupling

[Reaction: see text]. Small peptides having a 3-bromobenzyl group at the C-termini and n-alkynoyl group at the N-termini undergo a smooth copper-free intramolecular Sonogashira coupling reaction to afford the corresponding cyclic peptides in moderate yields. Scope and limitations of this macrocyclization is demonstrated with di-, tri-, and tetrapeptides.     

A mild and efficient method for the synthesis of vinylogous carbamates from alkyl azides

A mild and efficient one-pot method for the synthesis of vinylogous carbamates is reported starting from alkyl azides under a hydrogen atmosphere using 10% Pd/C. The resulting products are useful intermediates for the synthesis of heterocyclic compounds, natural products, and in peptidomimetics.     

Development and substantiation of a liquid chromatographic method for monitoring organic reactions involved in synthesis of 4-methoxyphenylacetic acid

A simple and rapid reversed-phase high-performance liquid chromatographic method for monitoring the reactions involved in two different processes for the production of 4-methoxyphenylacetic acid (PMPA) was developed. Impurity profiles of PMPA were used for fingerprinting of the two different synthetic processes by HPLC. Impurities were separated and determined on a Hypersil C18 column with acetonitrile-0.1 M potassium dihydrogen orthophosphate-triethylamine (40:59.95:0.05, v/v) (pH 3.0) as the mobile phase and detection at 280 nm at ambient temperature. The method was substantiated with respect to accuracy, precision, linearity, robustness, limit of detection and quantification. The method was found to be suitable not only for monitoring the reactions but also for quality assurance of PMPA as it could detect impurities at the level of 4 x 10(-9) g.     

DDQ mediated stereoselective intermolecular benzylic CN bond formation: Synthesis of (−)-cytoxazone, (−)-4-epi-cytoxazone and their analogues and immunological evaluation of their cytokine modulating activity

A short and efficient strategy for the synthesis of (?)-cytoxazone, (?)-4-epi-cyoxazone and their analogues by using DDQ mediated diastereoselective intermolecular benzylic amination has been described. Immunological evaluation of their cytokine modulating activity revealed that the change of hydroxy methyl to methyl group increased the cellular immunity in in-vitro cultures. Changes in the stereochemistry of oxazolidine haven't influenced the biological activity.