Ajit C. Kunwar

FERROUS SAPONITE FROM THE DECCAN TRAP, INDIA, AND ITS APPLICATION IN ADSORPTION AND REDUCTION OF HEXAVALENT CHROMIUM

Abstract A green-colored clay mineral occurring on the walls of amygdaloidal cavities and along fractures in the Deccan flood basalts at Killari, Maharashtra, India has been identified as iron-rich saponite, with chemical composition (Na0.60K0.04Ca0.47)(Mg2.05Fe2+3.95)(Si6.45Al1.55)O20(OH)4. The XRD data of the Killari sample with d (001) = 1.70 nm and b0 = 0.9275(2) nm conform to that of ferrous saponite. The FTIR spectra show vibrational bands typical of trioctahedral smectites. Differential thermal and thermogravimetric analyses show strong endothermic peaks due to dehydroxylation at 390-420 and 1070-1130 K accompanied by weight losses of 17 and 2.3 wt%. A weak exothermic peak at about 1220 K is also observed. These peaks are characteristic of smectites. 29Si and 27Al MAS NMR studies show that silicon and most of the aluminum in the clay mineral are in fourfold coordination. We have demonstrated for the first time the usefulness of ferrous-saponite in reduction of hexavalent chromium. X-ray photon electron spectroscopic (XPS) studies of the fine clay sample treated with dichromate solution show that this ferrous saponite has the capability of adsorbing and reducing hexavalent chromium to the trivalent state.

An approach towards the C1–C16 fragment of antineoplastic macrolide bryostatins by kinetic resolution of a racemic terminal epoxide using Jacobsen's catalyst

Abstract A stereo- and enantioselective approach towards the C 1 –C 16 fragment of bryostatins is reported using Jacobsens catalyst for kinetic resolution of a terminal epoxide, a Horner–Wadsworth–Emmons coupling reaction and a 1,4-Michael type cyclization as key steps.

Mandapamate, a diterpenoid from the soft coral sinularia dissecta

Mandapamate (3) is a diterpene with an unusual carbon skeleton from the soft coral Sinularia dissecta. The structure of mandapamate(3) was elucidated by interpretation of spectral data, particularly extensive NMR experiments, and was supported by a mechanistic hypothesis for its formation and molecular modelling.

Synthesis and Structure of α/δ-Hybrid Peptides—Access to Novel Helix Patterns in Foldamers

Stimulated by an overview on all periodic folding patterns of alpha/delta-hybrid peptides with 1:1 alternating backbone provided by ab initio molecular orbital theory, the first representatives of this foldamer class were synthesized connecting novel C-linked carbo-delta-amino acid constituents and L-Ala. In agreement with theoretical predictions, extensive NMR spectroscopic analyses confirm the formation of new motifs of 13/11-mixed helical patterns in these peptides supported by the rigidity of the D-xylose side chain in the selected delta-amino acid constituents. Relationships between possible helix types in alpha/delta-hybrid peptides and their counterparts in other 1:1 hybrid peptide classes and native alpha-peptides are discussed; these indicate the high potential of these foldamers to mimic native peptide secondary structures. The design of alpha/delta-hybrid peptides provides an opportunity to expand the domain of foldamers and allows the introduction of desired functionalities through the alpha-amino acid constituents.

InCl3-Catalyzed hetero-Diels–Alder reaction: an expeditious synthesis of pyranoquinolines

Indium trichloride catalyzes efficiently the cycloaddition reactions of aryl amines with 3,4-dihydro-2H-pyran (DHP) under mild reaction conditions to afford the corresponding pyrano[3,2-c]quinolines in high yields with high diastereoselectivity.

LiBF4-catalyzed formation of fused pyrano- and furanobenzopyrans

Lithium tetrafluoroborate efficiently catalyzes an unusual cyclization of o-hydroxybenzaldimines with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran at ambient temperature to afford a class of new pyrano- and furanobenzopyran derivatives in excellent yields with high diastereoselectivity.

Occurrence of natural fullerenes in low grade metamorphosed Proterozoic shungite from Karelia, Russia

Abstract We report on the occurrence of fullerenes in Proterozoic shungite (∼2 Ga) from the shungite mine, Kondopoga, Karelia, Russia (62.12°N 34.17°E). The presence of fullerenes has been confirmed by mass spectrometry, with peaks at 360 and 720 amu (atomic mass unit), powder X-ray diffraction showing ten diffraction peaks corresponding to the fullerite structure with a = 1.4201(5) nm, and 13 C nuclear magnetic resonance (NMR) spectroscopic studies, showing a peak at 143.2 ppm. In the Kondopoga shungite mine, fullerenes occur in silty shales that have experienced greenshist facies metamorphism.

InCl3-catalyzed stereoselective synthesis of C-glycosyl heteroaromatics

Abstract Glycals react smoothly with furan in the presence of a catalytic amount of indium trichloride at ambient temperature to afford predominantly the C -3-substituted glycals in high yields. Other heteroaromatics including 2 - benzyloxymethylfuran, thiophene and N -Boc protected indole afford exclusively C -1-glycosides in good yields with high β-selectivity under similar reaction conditions.

Synthesis and structural studies of oligomers of 6-amino-2,5-anhydro-6-deoxy-d-mannonic acid

Abstract A novel cycloetherification process involving a facile 5- exo S N 2-type ring closure by intramolecular opening of a terminal aziridine ring by a γ-hydroxyl group, led to the stereoselective synthesis of 6-amino-2,5-anhydro-6-deoxy- d -mannonic acid ( 1 ). Oligomerization of 1 by solution phase peptide coupling methods gave oligomers 2 – 5 . While most of the oligomers, in either protected or deprotected form, did not show any significant secondary structure, octamer 5 (P=H) exhibited a very strong positive band at 216 nm in its CD spectrum in MeOH and TFE, indicating the possibility of the presence of an ordered structure in solution. Its 1 H NMR spectra in various polar solvents, however, failed to produce any distinct dispersion of the amide proton chemical shifts. Compounds 1 – 5 were found to be inactive in hypoglyceamic tests in rats.

Towards the synthesis of (+)-discodermolide ☆

Abstract An approach to the asymmetric synthesis of fragments corresponding to C1C7 and C15C24 of (+)-discodermolide is reported. Key elements of the successful strategy include elaboration of two advanced fragments from a common precursor.