Basudeb Achari

Saponins from Albizia lebbeck

Three main saponins named albiziasaponins A, B, and C were isolated from the barks of Albizia lebbeck. Their structures were established through spectral analyses as acacic acid lactone 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)- beta-D-glucopyranoside, 3-O-beta-D-glucopyranosyl-(1-->2)-O-[alpha-L-arabinopyranosyl-(1-- >6)]- beta-D-glucopyranoside and 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)- O- [beta-D-glucopyranosyl-(1-->2)]-beta-D-glucopyranoside.

Expedient and rapid synthesis of 1,2,3-triazolo[5,1-c]morpholines through palladium-copper catalysis.

A one-pot approach using palladium-copper as catalyst has been developed for the synthesis of morpholines fused with 1,2,3-triazole. Good regioselectivity, mild reaction conditions, high yields and short reaction time are the hallmarks of this method.

A clerodane diterpene and other constituents of Clerodendron inerme

Abstract A new clerodane diterpene clerodermic acid was isolated from Clerodendron inerme and the structure deduced from spectral data. The known compounds friedelin, 5-hydroxy-7,4′-dimethoxyflavone, salvigenin, acacetin and apigenin were also found.

Two isomeric flavanones from vitex negundo

Abstract Two new flavanoids, characterized as 5,3′-dihydroxy-7,8,4′-trimethoxyflavanone and 5,3′-dihydroxy-6,7,4′-trimethoxyflavanone, have been isolated from the leaves of Vitex negundo.

Interaction of aristololactam-β-D-glucoside and daunomycin with poly(A): Spectroscopic and calorimetric studies

The binding of two sugar containing antibiotics viz. aristololactam-β-D-glucoside and daunomycin with single and double stranded poly(A) was investigated by spectroscopic and calorimetric studies. The binding affinity of daunomycin to ss poly(A) was of the order of 10⁶ M⁻¹ and that to ds poly(A) was of the order of 10⁵ M⁻¹. Aristololactam-β-D-glucoside showed a relatively weaker binding with an affinity of the order of 10⁴ M⁻¹ with both the conformations of poly(A). Fluorescence studies showed maximum quenching for daunomycin-ss poly(A) complexes. The binding constants calculated from fluorescence spectroscopy were in good agreement with that obtained from UV spectroscopy. Moderate perturbation of circular dichroic spectra of both the conformations of poly(A) in presence of these molecules with concomitant formation of prominent extrinsic CD bands in the 300-450 nm region further revealed the association. Isothermal titration calorimetry results showed an overall entropy driven binding in all the four systems though the entropy change was maximum in daunomycin-ss poly(A) binding. The binding affinity was also maximum for daunomycin-ss poly(A) and varied as daunomycin-ds poly(A) > aristololactam-β-D-glucoside-ds poly(A) > aristololactam-β-D-glucoside-ss poly(A). A 1:1 binding stoichiometry was observed in all the cases, as confirmed by Job plot analysis, indicating the interaction to consist of a single binding mode. Ferrocyanide quenching studies showed good stacking interaction in all cases but was best for daunomycin-ss poly(A) interaction. No self-structure formation was observed in poly(A) with both daunomycin and aristololactam-β-D-glucoside suggesting the hindrance of the sugar moiety for such structural organization.

Enantiospecific synthesis of 8-epipuupehedione from (R)-(−)-carvone

An enantiospecific synthesis of the antitumor marine sponge metabolite puupehedione (2a) and its C8-epimer 2b as their methylenedioxy derivatives 8a and 8b was achieved through concomitant O-allyl deprotection and electrocyclization of 20 derived from (−)-carvone.

A simple route to optically active, functionalized five-, six- and seven-membered carbocyclic derivatives

Abstract The isoxazolidinocarbocyclic derivatives 6, 7 and 13, useful as precursors for unnatural bioactive chiral carbocyclic nucleosides and for glycosidase inhibitors have been synthesized from D-glucose through intramolecular 1,3-dipolar cycloaddition.

Palladium-Catalyzed Approach for the General Synthesis of (E)-2- Arylmethylidene-N-tosylindolines and (E)-2-Arylmethylidene-N-tosyl/nosyltetrahydroquinolines: Access to 2-Substituted Indoles and Quinolines

A facile and efficient method for the synthesis of (E)-2-arylmethylidene-N-tosylindolines and (E)-2-arylmethylidene-N-tosyl/nosyltetrahydroquinoline variants has been developed through palladium-catalyzed cyclocondensation of aryl iodides with readily available 1-(2-tosylaminophenyl)prop-2-yn-1-ols and their higher homologues, respectively. The proposed reaction mechanism invokes the operation of trans-aminopalladation during cyclization (5/6-exo-dig), which ensures exclusive (E)-stereochemistry in the products. The method is fast, operationally simple, totally regio- and stereoselective, and versatile enough to access a variety of 2-substituted indoles and quinolines. The reactions proceeded efficiently with a wide variety of substrates and afforded the corresponding products in moderate to excellent yields.

An N-glycoside and steroids from Aristolochia indica

Abstract A phenanthrene derivative, aristololactam N-β- d -glucoside, and the steroids 3β-hydroxy-stigmast-5-en-7-one and 6β-hydroxy-stigmast-4-en-3-one have been isolated from Aristolochia indica.

Simultaneous Parallel and Antiparallel Self-Assembly in a Triazole/Amide Macrocycle Conformationally Homologous to d-,l-α-Amino Acid Based Cyclic Peptides: NMR and Molecular Modeling Study

A 1,4-linked triazole/amide based peptidomimetic macrocycle, synthesized from a triazole amide oligomer of cis-furanoid sugar triazole amino acids, possesses a conformation resembling the D-,L-α-amino acid based cyclic peptides despite having uniform backbone chirality. It undergoes a unique mode of self-assembly through an antiparallel backbone to backbone intermolecular H-bonding involving amide NH and triazole N2/N3 as well as parallel stacking via amide NH and carbonyl oxygen H-bonding, leading to the formation of a tubular nanostructure.