STEROIDS PART 1 ESTRANES, GONANES, AND ANDROSTANES

The bulk of the work on stracmre determination of steroids long predated the availability of any of the modern instmmental methods. The stmctures of the compounds were worked out entirely by classical noninstmmental methods that relied 

Strategies for Organic Drug Synthesis and Design, Second Edition. By Daniel Lednicer Copyright 2009 John Wiley Sons, Inc. 

All naturally occurring steroids, and the overwhelming majority of those used as drugs, comprise single enantiomers. When written as in the flow schemes that follow, the diagrams depict the absolute configuration. Substiments below the plane of these rather flat molecules are named a while those above that face are named (3, a convention that later spread to many other strucmral classes. 

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