Conformation of the C15 lupine alkaloids

Abstract

Methods have been developed for preparing 17[alpha]-deuterio-, 17[beta]-deuterio-, and 17-dideuteriolupanines. The nuclear magnetic resonance and infrared spectra of these provided strong evidence that ring C in the alkaloid is in a boat conformation in solution. Reduction of these compounds to the deuterated sparteines confirmed the same geometry for sparteine. In contrast, monodeutera-tion of aphylline at C-17 showed that it had an all-chair conformation in solution. 13[beta]-Hydroxylupanine was shown to have the same con-formation as lupanine in solution, but to adopt an all-chair conformation in the solid state. Interpretation of the nuclear magnetic resonance spectra enabled the conformation of ring C of 15-oxosparteine to be assigned. The oxidation and reductions involving C-17 of lupanine have been shown to be highly stereospecific, and an interpretation is given of the difference between the dehydrogenation of lupanine by mercuric acetate and those by N-bromosuccinimide or by the mercuric acetate ethylenediaminetetraacetic acid complex. It has now been found that the C-H stretching "trans bands" in the infrared are evident when only one hydrogen is alpha to the basic nitrogen and in an antiparallel re-lation to the lone pair of electrons.