Solution conformation of the thermolysin inhibitors carbobenzoxy-L-phenylalanine and beta-phenylpropionyl-L-phenylalanine and comparison of the solution conformation to the enzyme-bound conformation.

The conformations of enzyme inhibitors in solution and bound to the enzyme thermolysin are investigated as a convenient model for understanding the relationship between the conformation of drugs in solution and at the receptor. The solution conformations of carbobenzoxy-L-phenylalanine (I) and beta-phenylpropionyl-L-phenylalanine (II) are determined using nuclear magnetic resonance spectroscopy. These studies show that I and II have essentially the same conformation about both the alpha-beta bond and the C alpha-N bond in Me2SO-d6, acetone-d6, methanol-d4, chloroform-d, and D2O. In addition, the conformations of I and II are similar to phenylalanine and other phenylalanine derivatives. Comparison of the lowest energy solution conformer to that bound by the enzyme thermolysin shows that the lowest energy conformer (in solution) of carbobenzoxy-L-phenylalanine is bound by thermolysin; on the other hand, it is the highest energy conformer (in solution) of beta-phenylpropionyl-L-phenylalanine which is bound to the enzyme. This, to our knowledge, is one of the first experimental conformations of the hypothesis that an enzyme does not always bind the lowest energy conformer of an inhibitor.