CRYSTAL STRUCTURES OF HETEROCHIRAL PEPTIDES. PART II. TERT-BOC-VALYL-D-ALANYL-LEUCYL-ALANYL METHOXIDE

Crystal structure of a heterochiral peptide. viz. Boc-Val1-d-Ala2-Leu3-Ala4-OMe with a d chiral residue in the second position of a sequence, has been determined [a= 40.44(1), b= 4.887(5), c= 15.381(5) A, β= 109.6(1)°, space group C2, Z= 4, R= 0.11]. The peptide is in a parallel β-sheet structure terminated by a distinct local bend. The structure is stabilised by N–H⋯O as well as Cα–H⋯O hydrogen bonds. The contiguous Cα-H⋯O hydrogen bond observed in this structure is an unique observation. © Munksgaard 1991.