Hydrogen-bonding pathways affecting chemical reactivity of mandelylasparagine and related compounds

Abstract

The different behaviour of L-(+)-N-mandelyl-L-(–)-asparagine, N-mandelyl-2-amino-4-pentanoic acid and N-mandelyl-2-aminobutanoic acid towards acylation was considered. ¹³C and ¹H n.m.r. non-selective and selective relaxation rates and ¹H-{¹H} n.O.e.s were taken to show that L(+)-N-mandelyl-L-(–)-asparagine assumes, in DMSO solution, a conformation quite different from that of the other two amino acids. In this conformation both lone pairs of the alcoholic oxygen were shown to be involved in hydrogen bonding and to be shielded in a way that makes approach of the acylating reagent difficult.