Rina Ghosh

InCl3-induced C-glycosylation of per-O-acetylglycals with allyltrimethylsilane

Abstract InCl 3 has been used for the first time as a mediator for the C-glycosylation of per- O -acetylglycals with allyltrimethylsilane, and the reactions proceeded to give products in good-to-excellent yield and in high diastereoselectivity. The 1,5-anti diastereoselectivity in the allylation of 3,4,6-tri- O -acetyl-1,5-anhydro-2-deoxy- d - arabino -hex-1-enitol and 3,4-di- O -acetyl-1,5-anhydro-2,6-dideoxy- l - arabino -hex-1-enitol and the 1,4-anti diastereoselectivity with 3,4-di- O -acetyl-1,5-anhydro-2-deoxy- d - erythro -pent-1-enitol are in the range 80–90%, whereas 3,4,6-tri- O -acetyl-1,5-anhydro-2-deoxy- d - lyxo -hex-1-enitol furnished exclusively the corresponding C -α- d -galactopyranosyl compound.

K2CO3-Mediated, One-Pot, Multicomponent Synthesis of Medicinally Potent Pyridine and Chromeno[2,3-b]pyridine Scaffolds

Abstract An efficient one-pot, multicomponent synthesis of 3,5-dicyanopyridines has been developed from the reaction of malononitrile and different thiophenol or thiols with a variety of aldehydes (aromatic including hindered ones, heteroaromatic, and aliphatic) in the presence of 20 mol% of K2CO3 in refluxing 50% aqeuous ethanol. KMnO4 has been utilized as a readily available, inexpensive oxidant for the in situ transformation of the initially formed dihydropyridine intermediate. K2CO3 also mediates the one-pot formation of chromeno[2,3-b]pyridines from reaction of salicylaldehyde or its analogs with malononitrile and thiol or thiophenols. Both of these conditions also work equally well under 50-fold scale-up conditions. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT

Conformational and steric requirements of the side chain for sulphur participation in benzthiepin derivatives

Abstract Attempted ring expansion of some benzthiepin derivatives resulted in the formation of benzthiophens such as (3a,b) and (3d,e). A probable mechanism for this transformation has been presented.

Synthesis of novel aminoquinonoid analogues of diospyrin and evaluation of their inhibitory activity against murine and human cancer cells

The synthesis and tumor-inhibitory activity of a series of aminonaphthoquinone derivatives of diospyrin, which was isolated from Diospyros montana Roxb., are presented here for the first time. An aminoacetate derivative showed the maximum (approximately 93%) increase in life span in vivo against murine Ehrlich ascites carcinoma (EAC) at a dose of 1 mg kg(-1)day(-1) (ip; five doses), and the lowest IC50 (0.06 microM) in vitro. Further, the same analogue also exhibited considerable enhancement in antiproliferative activity when evaluated against human cell lines, viz. malignant skin melanoma and epidermoid laryngeal carcinoma (IC50=0.06 and 0.92 microM, respectively) in comparison to the natural precursor, diospyrin (IC50=0.82 and 3.58 microM, respectively). Moreover, diospyrin and all its derivatives were found to show significantly greater (approximately 17- to 1441-fold) cytotoxicity against the tumor cells as compared to normal human lymphocytes. All these quinonoids generated substantial amounts of reactive oxygen species in EAC cells, more or less commensurate to their respective IC50 values.

In(OTf)3—A New Efficient Lewis Acid Catalyst for Stereoselective C-Glycosylation Reactions of Glycal Derivatives

Abstract A variety of glycal derivatives reacted smoothly with allyltrimethylsilane and trimethylsilylcyanide in neat condition as well as in dichloromethane in the presence of 2–5 mol% of In(OTf)3 affording the corresponding 2,3-unsaturated C-glycosides in excellent yields and moderate to excellent α-selectivities.

Aryl 4,6-O-arylidene-1-thio-β-d-glycopyranoside-based new organogelators and their gels

Aryl 4,6-O-arylidene-1-thio-beta-d-glycopyranosides based on glucose and galactose form organogels in benzene, toluene, o- and p-xylene and 1,2,3,4-tetrahydronaphthalene. The gel morphologies of micro and nano dimensions were studied using SEM and TEM. Absorption spectroscopic studies of two organogels in benzene revealed that CH-pi or pi-stacking along with intermolecular H-bonding is responsible for the gel assembly.

Structure of the β-d-galactan isolated from the pods of Dolichos lablab Linn.

Abstract Hot-water extraction of the chlorophyll-free pods of Dolichos lablab Linn. furnished a mixture of polysaccharides containing mainly GalA and Gal, along with smaller proportions of Glc, Ara, and Rha. The mixture was fractionated by treatment with calcium chloride, followed by chromatography through a column of DEAE-cellulose (phosphate), to yield a β- d -galactan ( 1 ) containing Gal (95.6%) and a trace of GalA. Methylation analysis of 1 furnished 2,3,4,6-tetra-, 2,3,6-tri-, and 2,3-di- O -methyl- d -galactose in the molar ratios of 1:28:0.88. On periodate oxidation, 1 reduced 0.91 mol of the oxidant per hexosyl residue, and liberated one mol of formic acid per 29.4 mol of galactosyl units. Smith degradation of 1 furnished mainly threitol. From these results, and from enzymic reactions and spectroscopic data, a structure is suggested for the repeating unit of 1 . The M n of permethylated 1 was determined to be 1.206 × 10 4 .

A new triterpenoid saponin from Glinus oppositifolius with α-glucosidase inhibitory activity

Evaluation of α-glucosidase inhibitory activity led to the isolation of six triterpene saponins from the aerial parts of Glinus oppositifolius including one new and five known constituents. The structure of the new saponin, glinoside C (1), was established as 16-O-(β-D-glucopyranosyl)-3β,12β,16β,21α,22-pentahydroxy hopane by extensive use of 1-D, 2-D NMR and mass spectral techniques. The other constituents identified were 3-O-(β-D-xylopyranosyl)-spergulagenin A (2), spergulacin (3), spergulin A (4), spergulacin A (5) and spergulin B (6). Compound 1 exhibited the greatest inhibition of the enzyme with IC50 of 127 ± 30 µM. Kinetics study for the compound 1 demonstrated mixed type of inhibition (Ki = 157.9 µM).

ZrOCl2•8H2O-Catalyzed One-Pot Multicomponent Synthesis of β′-Acetamido-β-dicarbonyl Compounds with Special Reference to pref-Selective β′-Acetamido-β-ketoesters

Abstract ZrOCl2 · 8H2O catalyzes the one-pot synthesis of β′-acetamido-β-dicarbonyl compounds in high yields from aldehyde, enolizable β-dicarbonyl compound, acetyl chloride, and acetonitrile in solvent as well as in solvent-free conditions. β′-Acetamido-β-ketoesters are formed in moderate to exclusive pref-diastereoselectivity.

Trichloroisocyanuric acid (TCCA): an efficient green reagent for activation of thioglycosides toward hydrolysis

Trichloroisocyanuric acid (TCCA), an inexpensive, commercially available, and non-toxic reagent has been used for the activation of thioglycosides toward their hydrolysis to the corresponding hemiacetals in high to excellent yields. The methodology provides a mild reaction condition for dealing with compounds containing acid sensitive functional groups.