Relations between optical rotatory power and constitution in the steroids

The group of biologically important compounds containing the reducedcyclo pentenophenanthrene ring system (the “steroids”) provides a field for the exploration of relations between optical rotatory power and constitution which has hitherto received little attention. In the present paper a preliminary survey has been made of the scattered data in the literature with the object of finding in the first place whether constant partial rotations can be assigned to certain carbon atoms and groups. Even with compounds of established constitution the results are not by any means so concordant as those obtained by Hudson with many of the series of carbohydrates, but there is indubitable evidence of regularity, in spite of the fact that many of the determinations recorded are of a low order of accuracy, have been made with impure specimens of materials notoriously difficult to purify, or are discordant among themselves. For numerous substances determinations of optical activity under conditions which allow comparison with related compounds are lacking, and it is to be hoped that such evidence of regularity as is brought forward in this communication will lead to the filling of some of these gaps. The steroid skeleton, with an indication of the system of numeration adopted, is shown in fig. 1. A number of pairs of compounds are known in which there are opposite configurations of carbon atoms 3, 4, 5, and 17, and we have investigated whether it is possible to apply to these a rule analogous to Hudson’s “first rule of isorotation”,i. e ., whether the partial rotations of carbon atoms 3, 4, 5, and 17, as measured by the effect of reversing the configuration, are affected by changes in the structure of the remainder of the molecule. In Tables I-IV are summarized the data collected, with three exceptions, from the literature for the specific rotations of these diastereoisomeric pairs of compounds, determined for the D line and, as far as possible, the same solvents. Where more than one determination exists, the values of [α]D are, in general, the means of the recorded figures for presumably pure compounds, and no attempt has been made to select them critically. The last two columns show the differences of [α]D and the differences of [M]D ([M]D being defined as [α]D x (mol. wt.)/100); ∆[M]D corresponding to twice the partial rotation of the carbon atom concerned.