Abstract: Pentapeptides having the formula H-Asp-Ser-C-Pro-Arg-OH, where Asp, Ser, Pro and Arg may have L- or D-configuration, and C denotes Asp or Asn in L or D configuration, are synthesized by reacting in an aqueous medium Y.sub.2 -Pro-OH, wherein Y.sub.2 is a protective group, with Arg-Ro, wherein Ro is OH or is as defined below for R.sub.1 below, to form Y.sub.2 -Pro-Arg-Ro, which is deprotected, if necessary under conversion to Pro-Arg-R.sub.1, wherein R.sub.1 is an enzymatically cleavable .alpha.- carboxy substituting group selected form esters, amides, anilides, hydrazides or L-amino acid esters, and thereafter reacting Y.sub.3 -C(Z.sub.3)-OH with Pro-Arg-R.sub.1 to form Y.sub.3 -C(Z.sub.3)-Pro-Arg-R.sub.1 which is deprotected to C-Pro-Arg-R.sub.1, and then reacting Y.sub.4 -Ser-OH with C-Pro-Arg-R.sub.1 to form Y.sub.4 -Ser-C-Pro-Arg-R.sub.1, which is deprotected to Ser-C-Pro-Arg-R.sub.1, and reacting Y.sub.5 -Asp(Z.sub.5)-OH with Ser-C-Pro-Arg-R.sub.1 to form Y.sub.5 -Asp(Z.sub.5)-Ser-C-Pro-Arg-R.sub.

Abstract: The B-30 amino acid in insulins is replaced enzymatically byreacting as substrate component the selected insulin Ins-X, wherein X represents the B-30 amino acidwith an amine component selected from the group consisting of(a) amino acids of the formulaH--B--OHwherein B is an amino acid residue,(b) optionally N-substituted amino acid amides of the formulaH--B--NR.sup.1 R.sup.2wherein B is an amino acid residue and R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen, amino, hydroxy, alkyl, cycloalkyl, aryl, heteroaryl and aralkyl or R.sup.1 and R.sup.2 together with the nitrogen atom form a heterocyclic group which may contain a further hetero atom, and(c) amino acid esters of the formulaH--B--OR.sup.3, H--B--SR.sup.3 or H--B--SeR.sup.3wherein B is am amino acid residue and R.sup.