Abstract Several representative peptides and peptide derivatives have been synthesized using an N-formyl blocking group and the carbodiimide coupling method. Racemization was not observed, and optimum conditions for acidic hydrolysis of the N-formyl function were determined. Similar custom peptide synthesis employing the mixed anhydride procedure led to extensive racemization. It has been shown that an N-formyl peptide ester can be extended on either the amino or carboxyl end by selective hydrolysis.
They have been successfully used in custom peptide synthesis, in both solution and solid phase. We have demonstrated that UNCAs are interesting starting materials for the synthesis of various amino acid derivatives. Chemoselective reduction of UNCAs with sodium borohydride led the corresponding N-protected beta amino alcohols. Reaction of UNCAs with Meldrum's acid, followed by cyclisation, yielded enantiomerically pure tetramic acid derivatives. Diastereoselective reduction of tetramic acid derivatives produced [4S,5S)-N-alkoxycarbonyl-4-hydroxy-5-alkylpyrrolidin-2-ones derived from amino acids, which after hydrolysis yielded statine and statine analogues.
Tetramic acid derivatives could also be obtained by reaction of UNCAs with benzyl ethyl malonate in the presence of sodium hydride to yield gamma-N-benzyloxycarbonylamino-beta-oxodicarboxyl esters followed by hydrogenolytic deprotection and decarboxylation. UNCAs also reacted with phosphoranes to produce the ketophosphorane in excellent yields. Subsequent oxidation with oxone or with [bis(acetoxy)-iodo]-benzene produced vicinal tricarbonyl derivatives. These reactions usually proceeded smoothly and with high yields.