Simplification of the induced circular dichroism method and its application to biologically active natural products

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1) Circular dichroism in a chiral amide possessing an achiral bhaohthyl chromophoreThe bisignate CD curves were observed at around 240 nm in all binaphthyl amides examined. In a conformational analysis of the derivatives, a close correlation was observed between the signs of exciton chirality and the screw senses of the two 2-naphthoyl groups (positive/clockwise; negative/counterclockwise). A semi-empirical molecular orbital calculation (AM1) suggested an intramolecular hydrogen bonding. The CD spectra of the antipodal amides changed into split curves centered at 225 nm after N-methylation. Furthermore, the calculated screw senses between the electric transition moments of the binaphthyl system in N-methyl amides were in good accordance with those expected from their exciton chiralities, indicating a possible application for determination of absolute configuration.2) Induced circular dichroism and conformational analysis of 2.2'-binaphthyl esters derived from primary alcohols possessing a stereogenic center in the β-positionInduced bisignate CD curves were observed near 240 nm in all 2, 2'-binaphthyl esters derived from primary alcohols with a chiral center in the p-position of the hydroxyl group. Conformational analyses of the esters by molecular mechanics were performed. In some cases, the calculated screw sense between the two longitudinal transition moments of 2-naphthoate groups for the most stable conformer with clockwise or counterclockwise orientation was found to be different from that expected from their exciton chiralities. Therefore, CD calculations and conformational analyses of the two esters having strong or moderate interaction between the functional group of the substrate and the ester group of the 2-naphthoate were carried out by the time-dependent density functional theory (TD-DFT). The results suggested that the TD-DFT is strongly effective for determination of the absolute configuration of binaphthyl esters.