Padmanava Pradhan

Norditerpene furan glycosides from Tinospora cordifolia

Abstract Two new norditerpene furan glycosides (cordifoliside D and cordifoliside E) were isolated, as their tetraacetates, from the polar butanol extract of Tinospora cordifolia stems. The structural elucidations and relative configurations are based on high-resolution 1D and 2D NMR spectroscopy.

Cordifolisides A, B, C: Norditerpene furan glycosides from Tinospora cordifolia

Several glycosides were isolated, as polyacetates, from the n-BuOH fraction of the Tinospora cordifolia stems. The structures of three new norditerpene furan glycosides cordifoliside A, B and C have been established by 1D and 2D NMR spectroscopy.

Electron donor-acceptor interactions of C60 with n-and π-donors : A rational approach towards its solubility

Abstract Investigations on molecular interactions of C60 with a variety of solvents show that its solubility is largely controlled by efficient charge transfer interactions between electron deficient C60, with suitable n-and π-donors. Organic species having a lone pair of electron on heteroatoms (n-donors) and/or π-electron cloud (π-donors) which are capable of forming charge transfer complexes with C60, are better solvents. Solvent-C60 interaction studies thus help in the rational design of solvents and has led to the discovery of several new classes of solvents such as brominated aliphatic hydrocarbons, nitrogen heterocycles, alkylated aromatics, aryl-alkyl ethers and bromoaryl-alkyl ethers. A detailed NMR study gave insight into the nature of molecular interactions.

Stereo- and regioselectivity of intramolecular 1,2-arene-alkene photocycloaddition in 2-alkenyl-4-chromanones

Abstract Intramolecular 1,2-arene-alkene photocycloaddition of 2-alkenyl-4-chromanones gave complex multicyclic oxatetracyclotetradecanediones which on internal photo- and microwave induced thermal rearrangements provided a diverse array of compounds with [3.3.0]bicyclooctane carbon frame work. The stereo- and regiochemical aspects as well as desymmetrization of alkenyl chromanones due to intramolecular 1,2-arenealkene photocycloaddition have also been discussed.

A novel intramolecular 1,2-arene-alkene photocycloaddition

A novel intramolecular 1,2-arene-alkene photocycloaddition of 2-alkenyl-7-hydroxy-4-chromanone(1) and its alkyl ethers (2 and 3) to (4α, 7α, 9α)4,8,8-trimethyl-14-oxatetracyclo(6.5.14,13.01,9)tetradeca-12-ene-2,11-dione (4) is described.

NOVEL CYCLOBUTANE FUSED FUROCHROMONE OLIGOMERS FROM THE SEEDS OF PIMPINELLA MONOICA DALZ

Abstract Novel oligomers viz. di-, tri-, tetra- and pentamers (2–5) of the furochromone visnagin (1) were isolated from the chloroform extract of the fresh mature seeds of the plant Pimpinella monoica. 1D and 2D NMR studies revealed a linear head-to-tail (2 + 2) pyran-furan fusion for the oligomers. NOE data and molecular modelling suggested that the higher oligomers with all syn geometry may have helicity.

A novel intramolecular arene–alkene photocycloaddition in 2-alkenyl naphtha-4-chromanones—a short route to functionalised multicyclic systems

On irradiation, 2-methyl-2-ethenyl naphtha-4-chromanone 1 undergoes an unusual intramolecular arene–alkene photocyclisation, followed by rearrangements to give a [5.3.1.06,1]benzotricycloundecene, 5.

Intramolecular photorearrangement of a 2-alkenyl-4-chromanone to an oxapentacyclotetradecanedione

Abstract A novel transformation of 7-hydroxy-2-methyl-2-(4-methyl-3-pentenyl)-4-chromanone ( 1 ) to intramolecular 1,3-arene-alkene photocycloadduct, (1 S ,2 R ,5 S ,7 S ,10 S ,13 R )6,6,10-trimethyl-14-oxapentacyclo[8.3.1.0 1,7 .0 2,13 0 5,13 ] tetradecane-3,12-dione ( 3 ) via secondary photorearrangement of 1,2-arene-alkene photocycloadduct ( 2 ) has been described.

STEREOCHEMICAL ASSIGNMENT OF TERTIARY HYDROXYL GROUP IN DITERPENE FURAN GLYCOSIDES BY PYRIDINE INDUCED SHIFTS, 13C- AND 2D-NMR SPECTROSCOPY

Abstract The stereochemistry of the tertiary hydroxyl group in diterpene furan glycosides viz. cordifolisides D (1) and cordifoliside E (2) has been assigned on the basis of pyridine solvent induced shifts (PIS) in the 1H and 13C NMR spectra. The methyl and the methylene groups occupying positions vicinal, 1,3-diaxial and geminal to the tertiary hydroxyl group were deshielded to different extent depending on the dihedral angle. The stereochemical assignments are well supported by 13C-γ shifts and 2D Overhauser spectroscopy.

Structure of zeyloxanthonone (wightianone)- a reinvestigation.

Abstract The structure of zeyloxanthonone has been unambiguously established as 1,2,3,4- tetrahydro- 6,8- dihydroxy- 1,1,7- tris (3- methyl but-2- enyl)- xanthene-2,9- dione (1) by 2D NMR spectroscopy, isotopic exchange and chemical reactions.