Derivatives of the lactam of α-guanidinoglutaric acid ( N-amidinopyroglutamic acid, ApGlu) for peptide formation

Abstract

Methods are described for the preparation of the tosyl, N-tert-butoxycarbonyl (BOC), and carbobenzoxy (CBZ) derivatives of 1-amidino-2-pyrrolidone-5-carboxylic acid ( N-amidinopyroglutamic acid, ApGlu) to be used as an end group for bioactive peptides. The derivatives were formed by the reaction of ApGlu with toluenesulfonyl chloride for the tosyl, benzylformoyl chloride for the CBZ, and t-butylformoyl chloride for the BOC derivative. Strong alkali (pH 12–13) is necessary to carry out the reaction, and the reaction does not take place below 15 °C. In each case the major product is the diacyl derivative. These derivatives form esters readily with nitrophenol, pentachlorophenol, and pentafluorobenzyl phenol in the presence of N,N′-dicyclohexycarbodiimide (DCI). The pentachlorophenyl ester was preferred because of a high yield and ease of crystallization. These esters react with glycyl proline amide (as an example of a peptide) to form the protected tripeptide. The diacyl derivatives of ApGlu also react directly with glycyl proline amide in the presence of DCI. Anhydrous HCl or HBr cannot be used to free the peptide since it strips off the amidino group. Reduction of the CBZ derivative with Pd on BaSO 4 was effective in this regard but the tripeptide formed was unstable.