Synthesis of arginine aldehydes for the preparation of pseudopeptides

The synthesis of optically active aldehydes from N alpha-Boc-amino acids by reduction of the corresponding O,N-dimethyl-hydroxamates, while proceeding smoothly for most amino acids, has presented significant problems in the case of arginine. We demonstrate here that this difficulty can be overcome by the use of arginine derivatives in which the guanidino group is completely protected, such as in the case of N alpha-Boc-Arg(di-Z). In the case of nitro-, tosyl- or pmc-protected arginine, no satisfactory aldehyde formation can be obtained. It appears that in these cases the guanidino group is insufficiently protected and inhibits the formation of aldehydes. We also demonstrate that aldehydes can be readily obtained from N alpha-Fmoc protected amino acids.