13C NMR spectra and structure of azasteroids with an N-acylamidine fragment in the D ring

Abstract

1. The13C and1H NMR spectra of isomeric steroids of the 17-aza and 17a-aza series with an amidine fragment in the D ring have been investigated. 2. The13C chemical shifts make it possible to identify isomeric steroids and to determine the position of the double bond in the amidine fragment. It has been shown that compounds with a single substitution in the amidine fragment exist in the acylimine form, while the disubstituted compounds exist in acyl- and diacylamide forms. The acylimine form forms a cyclic intramolecular hydrogen bond of the NO=O...HN type. 3. The γ effects of an =NR group in the D ring in an eclipsed conformation are similar to the γ effect of the oxygen atom in a carbonyl group in D-homoandrostanes. 4. The rotation of a 17a-diacylamide group, unlike that of a 17-acylamide group, is hindered.