CONFORMATIONAL ANALYSIS OF N-TERT AMYLOXYCARBONYL-L PROLINE IN THE SOLID STATE AND IN SOLUTION

Solid-state conformational analysis of N-tert-amyloxycarbonyl-L-proline indicated that the molecules are not folded up to form an oxy-C7 peptide conformation, but are held together through intermolecular O-H .... O .dbd. C (urethane) H-bonds. The tertiary amide bond is in the cis configuration. In solvents of high polarity strongly solvated species largely predominate. In cyclohexane solution non-associated and associated (involving the carboxyl C .dbd. O as the proton acceptor) species are simultaneously present. The extent of association increases with increasing solute concentration. The amount of the oxy-C7 form, if any, should be extremely small. It is also demonstrated that circular dichroism measurements alone can lead to an incorrect picture of the conformational preferences of amino acid derivatives and small peptides in solution.