Studies on the disproportionation of mixed anhydrides of N‐alkoxycarbonylamino acids

Abstract

Mixed anhydrides from Z‐valine and ethyl, isobutyl, isopropyl and isopropenyl chloroformate, and from N‐tert‐butoxycarbonyl‐ (Boc) and N‐benzyloxycarbonyl‐ (Z) leucine and phenylalanine and Boc‐ and N‐9‐fluorenylmethoxycarbonyl‐valine and ethyl chloroformate were purified and left in dichloromethane at 23°C. The symmetrical anhydride (SyAn) generated after 24 h was determined by normal phase high‐performance chromatography. No SyAn was produced from the anhyrides of Z‐ and Boc‐valine; SyAn was produced from the other anhydrides. Anhydrides examined without isolation generally produced more SyAn than the pure compounds. More SyAn was generated in dimethylformamide and tetrahydrofuran than in dichloromethane, or in the presence of an excess of N‐methylmorpholine or triethylamine. The anhydride from isobutyl chloroformate was much more stable than the anhydride from ethyl chloroformate. It is suggested that disproportionation of pure mixed carboxylic acid – carbonic acid anhydrides occurs by a bimolecular mechanism.

Anhydride-Based Reconfigurable Shape Memory Elastomers

“…In separate studies, one of us introduced biodegradable elastomers utilizing thiol–ene “click” chemistry and incorporating hydrolytically labile anhydride groups . For our present study, we postulated that the anhydride groups of the elastomeric matrix might enable desired exchange reactions for thermal reconfiguration based on limited (and often old) literature that indicated such exchange reactions occur in solution, though no prior report testing this notion in solid or rubbery materials could be found to support our conjecture. − In this report, we present the synthesis and characterization of a new soft, shape memory elastomer that is thermally reconfigurable, termed Re-SMEC.…”

Preparation of activated esters of N-alkoxycarbonylamino and other acids by a modification of the mixed anhydride procedure

“…Na2C03 (1.45 equiv.) in DMF-H20 (4:1), and the mixture was stirred for 8 h (29). DCM (10 mL) and 5 aq.…”

“…The optical integrities of Boc-Val-ONp and Z-Phe-ONp were established by aminolysis of the esters with H-D-Phe-OEt in DCM-DMF (4: 1) followed by analysis of the epimeric peptides by NP-HPLC (Table 1). The optical integrities of Boc-Leu-ONSu, Boc-Leu-OPfp, Z-Leu-ONp and Z-Val-ONp were established similarly by RP-HPLC after aminolysis by D-valine (29).…”