Application of Optical Rotatory Dispersion Studies to Problems in Natural Products Chemistry. Lv*

Modern natural products chemistry-in terms of isolation, structure elucidation, determination of relative and absolute configuration, and finally chemical or biological synthesis-covers more facets of organic chemistry than any other single area of this science. The remarkable progress which has been achieved in this field during the past twenty years can be ascribed, to a considerable extent, to the eagerness with which the natural products chemist has been willing to employ techniques which were either developed for his specific purpose or, more frequently, discovered in another connection but clearly helpful to his own needs. For instance, at the isolation stage, one can hardly conceive ofa natural products laboratory that does not employ elution, partition, paper or gas-phase chromatography. At the next step, structure elucidation, the organic chemist dealing with natural products has always been very receptive to the use of physical methods which would offer him, rapidly, preliminary information to delineate the more profitable areas of chemical attack. These physical methods were invariably discovered by physicists or physical chemists, but their extensive application to organic chemistry was usually accomplished by a semi-empirical approach in which a great number of organic compounds were examined, and then the chemical structure and the particular physical property under discussion were correlated. Chronologically, ultra-violetspectroscopy was followed by infra-red absorption measurements, then nuclear magnetic resonance studies and, about the same time, by the more extensive use of mass spectrometry. In each case, the organic chemist, and especially the natural products investigator, accepted the particular physical method as soon as instrumentation became sufficiently advanced, so that these measurements could be conducted easily in or near his own laboratory. Furthermore, it should be noted that all of the above-mentioned physical measurements have invariably added information which was not available from the others, so that they have always tended to complement one another. We have, therefore, reached the point where most new natural products, after isolation, purification and elementary analysis, are subjected to a gamut of physical measurements before serious degradative efforts are initiated. Even during the * For paper LIV, see q. Djerassi, Endeavour, 20, 138 (1961).