Synthesis and L-type calcium channel blocking activity of new chiral oxadiazolothiazinones.

Oxadiazolo[3,4-c][1,4]thiazin-3-ones are cardiovascular agents that block L-type calcium channels. Previous data of cardiac and vasorelaxant activity on guinea-pig for several derivatives indicated the two positions ortho to the thiazine's sulphur as crucial for modulating the activity; but these positions are likely susceptible to metabolic biotransformations, as indicated by in silico predictions. We designed new derivatives, and obtained three negative inotropic agents with EC50 in the low nanomolar range, more potent than all the precursors published so far.

Absolute configuration assignment of norcamphor-derived furyl hydroperoxide using density functional theory calculations of optical rotation and vibrational circular dichroism.

Density functional theory (DFT) calculations of sodium d line specific rotation and of vibrational circular dichroism (VCD) have been used to assign the absolute configuration of a recently prepared (1S,4R)-norcamphor-derived furyl hydroperoxide, (+)-3, introduced as a stereoselective oxidant. Both approaches give the same absolute configuration to the newly generated stereogenic carbon at position 2, i.e.

Electronic circular dichroism of monomethyl [16O,17O,18O]-phosphate and [16O,17O,18O]-thiophosphate revisited.

Phosphoryl-transfer reactions have long been of interest due to their importance in maintaining numerous cellular functions. A phosphoryl-transfer reaction results in two possible stereochemical outcomes: either retention or inversion of configuration at the transferred phosphorus atom. When the product is phosphate, isotopically-labeled [16O,17O,18O]-phosphate derivatives can be used to distinguish these outcomes; one oxygen must be replaced by sulfur or esterified to achieve isotopic chirality.

Stereoselective behavior of the functional diltiazem analogue 1-[(4-chlorophenyl)sulfonyl]-2-(2-thienyl)pyrrolidine, a new L-type calcium channel blocker.

We studied the stereoselective behavior of 1-[(4-chlorophenyl)sulfonyl]-2-(2-thienyl)pyrrolidine, a recently described blocker of cardiovascular L-type calcium channels that binds to the diltiazem site. Given the stereocenter at C-2 of the pyrrolidine ring, the two enantiomers were separated by chiral HPLC and, using VCD in conjunction with DFT calculations of chiroptical properties, the absolute configuration was assigned as R-(+)/S-(-). For both forms, functional, electrophysiological, and binding properties were studied and the three-dimensional superimpositions of the two enantiomers over diltiazem were obtained in silico.

Determination of the absolute configuration of the natural product Klaivanolide via density functional calculations of vibrational circular dichroism (VCD).

The absolute configuration (AC) of the antiprotozoal lactone, Klaivanolide, 1, from Uvaria klaineana, has been determined using Vibrational Circular Dichroism (VCD) spectroscopy. The experimental VCD spectrum of the (+) enantiomer of 1 was measured. To analyze the AC of (+)-1, the conformationally-averaged VCD spectrum of 7-S-1 was calculated using density functional theory (DFT) and the GAUSSIAN 03 program.

Determination of the absolute configuration of the sex pheromone of the obscure mealybug by vibrational circular dichroism analysis.

Comparison of theoretical and experimental vibrational circular dichroism (VCD) spectra of an enantiopure synthetic sample of the obscure mealybug sex pheromone allowed the determination of the absolute configuration of the insect's pheromone.

The determination of the absolute configurations of chiral molecules using vibrational circular dichroism (VCD) spectroscopy.

The vibrational circular dichroism (VCD) spectra of the two enantiomers of a chiral molecule are of equal magnitude and opposite sign: i.e. mirror-image enantiomers give mirror-image VCD spectra.

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: the iso-schizozygane alkaloids isoschizogaline and isoschizogamine.

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the concerted application of DFT calculations of VCD, ECD, and OR to the determination of the ACs of the isoschizozygane alkaloid natural products, isoschizogaline, and isochizogamine, whose ACs have not previously been determined. The ACs of naturally occurring (-)-isoschizogaline and (-)-isoschizogamine, are both determined definitively to be 2R, 7R, 20S, 21S.

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism and optical rotation: the schizozygane alkaloid schizozygine.

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the first concerted application of DFT calculations of VCD, ECD, and OR to the determination of the AC of a natural product whose AC was previously undetermined. The natural product is the alkaloid schizozygine, isolated from Schizozygia caffaeoides.

Calcium channel antagonists discovered by a multidisciplinary approach.

A multidisciplinary project has led to the discovery of novel, structurally diverse, L-type calcium entry blockers (CEBs). The absolute configuration of a recently reported CEB has been determined by vibrational circular dichroism spectroscopy, to assign the stereospecificity of the ligand-channel interaction. Thereafter, a virtual screening procedure was performed with the aim of identifying novel chemotypes for CEBs, starting from a database of purchasable compounds; 340,000 molecules were screened in silico in order to prioritize structures of interest for bioscreening.

Synthesis, chromatographic separation, vibrational circular dichroism spectroscopy, and ab initio DFT studies of chiral thiepane tetraol derivatives.

Optically pure enantiomers of the chiral tetrahydroxythiepane derivative 3,6-dihydroxy-4,5-O-isopropylidene-thiepane (3) are obtained using a novel protocol in which a library of all possible stereoisomers of 3 is synthesized, followed by two-step stereoselective chromatography, using, first, conventional achiral and, then, chiral stationary phases. Configurational and conformational analysis of 3 are carried out using Vibrational Circular Dichroism (VCD) spectroscopy in conjunction with ab initio DFT calculations. The absolute configuration of 3 is shown to be 3R,4S,5R,6R-(+)/3S,4R,5S,6S-(-).