Steroidal side chains absolute configuration

Absolute configuration at C-24 and C-25 in 24-methyl-26-hydroxy- and 24-methyl-26-oic steroidal side-chains. 

Similar NMR studies of MTPA esters showed that there was a correlation between the shape of the signals due to the CH2OH (C-26) group in the R) and (5)-MTPA esters and the absolute configuration at C-25. This new approach (i.e., comparison of the chemical shifts of the methylene protons at C-26 in the spectra of the R) and (S)-MTPA esters) has the advantage of avoiding the use of europium salts and has been widely used by researchers interested in the stereochemistry of steroid side chains. ... 

A full account has appeared of the study of absolute configurations of vicinal diols and amino-alcohols by c.d. measurements in solutions containing nickel acetylacetonate [Ni(acac)2] or the n.m.r. shift reagent [Pr(dpm)3]. Examples of steroidal derivatives examined include 2,3-, 3,4-, 5,6-, 16,17-, 17a,20j8-, and side-chain diols. 

The occurrence of a large variety of steroids with multiple oxygen functionalities and different alkylation patterns in the side-chains has often required the assignment of absolute configurations to chiral centers. In most cases this has involved the synthesis of appropriate models and the analysis of their H and C nmr spectra and of those of their derivatives with a chiral reagent. 

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