Conformation of the C₁₅ lupine alkaloids

Methods have been developed for preparing 17α-deuterio-, 17β-deuterio-, and l7-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, moilodeuteration of aphylline at C-17 showed that i t had an all-chair conformation in solution. 13β-Hydroxylupanine was shown to have the same conformation 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 betmeen the dehydrogenation of lupanine by mercuric acetate and those by Nbromosuccinimide or by the mercuric acetate - ethylenediatninetetraacetic 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 relation to the lone pair of electrons.

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