. . . "In other preferred embodiments, the compounds have formulae I or II, particularly formula I, as defined above, but with the proviso that: (1) at least one of the amino acid residues in the resulting di or tri-peptide is a non-naturally-occurring ??-amino acid or at least one of the R1, R3 and R5 is not a side chain of a naturally-ocurring amino acid; and (2) none of R1, R3 and R5 is the side chain" .