Structure elucidation of a new isoflavone by exclusive use of ¹H NMR measurements.

The leaves of Piscidia carthagenensis provided new 7,2',5'-trimethoxy-3',4'-methylenedioxyisoflavone (1), admixed with known 6,7-dimethoxy-3',4'-methylenedioxyisoflavone (2), and 5,4'-dihydroxy-7,2',5'-trimethoxyisoflavone (3), which were separated by extensive fractional solubillization. Selective irradiation of the H-5 "singlet" of 2 allowed distinction of the two methoxy group signals, whose chemical shift difference is only 0.004 ppm (1.2 Hz at 300 MHz). The (1)H and (13)C NMR data of 3 were assigned with the aid of HETCOR and gHMBC measurements. Although 1 looked inhomogeneous in the solid state, its solution structure followed from (1)H NMR measurements, where it looked homogeneous. To clarify the solid state aspect and confirm the structure of 1, two types of crystals were mechanically separated and subjected to single crystal X-ray diffraction measurements. This study revealed polymorphism because of the concomitant presence of orthorhombic and triclinic crystals, but showed no atropisomerism. The structure of 3 was also verified by X-ray diffraction crystallography.

Vibrational circular dichroism (VCD), VCD exciton coupling, and X-ray determination of the absolute configuration of an α,ß-unsaturated germacranolide.

The absolute configuration of was deduced by vibrational circular dichroism together with the evaluation of the Flack and Hooft X-ray parameters. Vibrational circular dichroism exciton coupling, using the carbonyl group signals, confirmed the absolute configuration of . In addition, sodium borohydride reduction of the 11,13-double bond of 6-epi-desacetyllaurenobiolide () yields an almost equimolecular mixture of C11 epimers, while reduction of the same double bond of 6-epi-laurenobiolide () provided almost exclusively the (11S) diastereoisomer .

Structure, absolute configuration, and antidiarrheal activity of a thymol derivative from Ageratina cylindrica.

The leaves of Ageratina cylindrica afforded a thymol derivative that was characterized by physical and spectroscopical methods as (8S)-8,9-epoxy-6-hydroxy-l0-benzoyloxy-7-oxothymol isobutyrate (1). The absolute configuration of 1 was established as 8S by vibrational circular dichroism spectroscopy in combination with density functional theory calculations and by evaluation of the Flack and Hooft X-ray parameters. Compound 1 showed weak antiprotozoal activity against Entamoeba histolytica and Giardia lamblia trophozoites and a high inhibitory effect on hyperpropulsive movement of the small intestine in rats.

Determination of absolute configuration of salvic acid, an ent-labdane from Eupatorium salvia, by vibrational circular dichroism.

The relative stereochemistry at C13 and the absolute configuration of salvic acid, a constituent of the leaves of Eupatorium salvia, were established as the 13-(R)-ent-labdane 1. The results follow from vibrational circular dichroism measurements of the derived O-methyl ether methyl ester 3 which were compared to DFT B3LYP/DGDZVP calculated spectra. The relative stereochemistry of salvic acid at C13 was independently verified by single crystal X-ray diffraction measurements of 1, and of its derived diol 4.

Synthesis of pyrrolidinoindolines from 2-(2-oxo-3-indolyl)acetates: scope and limitations.

A series of 1,3a,8-alkylpyrrolidinoindolines have been synthesized. The scope and limitations of the alkylation of starting methyl oxindol-3-acetates are explored employing electron-rich and electron-poor alkylating agents. Hydrolysis and reductive lactonization of the resulting carboxylic gamma-oxindolic acid derivatives proceeds with good yields to afford 2-oxofuroindolines providing ready access to the pyrrolidinoindoline derivatives.

Stereostructure reassignment and absolute configuration of isoepitaondiol, a meroditerpenoid from Stypopodium flabelliforme.

Careful examination of the published NMR data for isoepitaondiol, a meroditerpenoid from Stypopodium flabelliforme, suggests that its published structure 1 must be revised. On the basis of extensive 1D and 2D NMR studies, we now propose that structure 2, with a trans-anti-trans-anti-cis arrangement fits isoepitaondiol diacetate. The relative configuration of 2 was confirmed by single-crystal X-ray diffraction, while the absolute configuration was evidenced by vibrational circular dichroism in combination with DFT B3LYP/DGDZVP calculations.