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Free keywords:
ORGANIC-SOLVENTS; LIPASES; ACYLATION; PROTECTING GROUPS; LIPASES; PEPTIDES;
Abstract:
Amino acid (Hep) esters are accessible as generally crystalline hydro tosylates 3 from the amino acids by azeotropic esterification with 1-heptanol in high yields. They can be condensed with Z-, Boc-, and Aloc-protected amino acids to give the dipeptides 7-9 in the presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). From the fully protected dipeptides the N-terminal protecting groups are cleaved by chemical methods without affecting the Hep esters. On the other hand, the heptyl esters can be hydrolyzed under mild conditions (pH = 7.0, 37-degrees-C) and with high yields by means of a lipase from Rhizopus niveus without attacking the N-terminal urethane groups or the peptide bonds.
