反应详情

Coupling of the tosylate salt of benzyl glycinate with acid 9 proceeded smoothly to give the protected acyclic precursor 12, Scheme 5. Simultaneous hydrogenolysis of the Cbz and Bn protecting groups followed by cyclization with diphenylphosphoryl azide (DPPA) in dilute DMF solution afforded cyclic tripeptide methyl ester 13 in high yield.40In anticipation of future incorporation of amino acids beside Gly into the mimic, DPPA was chosen for cyclization because of the low propensity of acyl azides to racemize.41This cyclization has also been performed with Ala in the central position in 80% yield. ##STR6##

1. customto give the protected acyclic precursor 12, Scheme 5