Abstract: Human insulin or B-30 esters thereof are prepared by reacting an insulin derivative of the formula ##STR1## wherein R is hydroxyl or an amino acid radical being different from threonine, and -A- and -B- represent the A- and B-chains with the same amino acid sequence as in human insulin, with a carboxyl protected and optionally hydroxyl protected L-threonine derivative in a concentration of from 2 to about 6 moles per liter in the presence of trypsin or a trypsin-like enzyme in a reaction medium containing water and optionally also an organic cosolvent at a pH value of from 5 to 9 and at a temperature below 50.degree. C., followed, if desired, by removal of any protecting groups present.Human insulin is prepared in an easy and simple way in high yield and in high purity.

Abstract: Polypeptide derivatives of the formula:a--x--b--y--cwherein x represents an acidic amino acid, preferably glu or asp,y represents a basic amino acid, preferably arg, lys or his,z represents hydrogen or a small protective group for the .alpha.-amino group in x,b represents a bond, a single amino acid or a peptide having up to 10 amino acids in the chain, andc represents --NR.sup.1 R.sup.2, wherein R.sup.1 and R.sup.2 are selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl and C.sub.3 -C.sub.8 cycloalkyl, or R.sup.1 and R.sup.2 together with the attached nitrogen atom form a heterocyclic group optionally containing an additional hetero atom, orc represents --OR.sup.3, wherein R.sup.3 is selected from the group consisting of C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, benzyl, phenacyl, phthalimidomethyl, .beta.

Abstract: Polypeptide derivatives of the formula:a--x--y--arg--leu--dwhereinx represents a bond, a single amino acid or a peptide having up to 10 amino acids in the chain,y represents gln- glu or glu,a represents hydrogen or a small protective group for the .alpha.-amino group in the N-terminal amino acid,d represents --NR.sup.1 R.sup.2, wherein R.sup.1 and R.sup.2 are selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl and C.sub.3 -C.sub.8 cycloalkyl, or R.sup.1 and R.sup.2 together with the attached nitrogen atom form a heterocyclic group optionally containing an additional hetero atom, ord represents --OR.sup.3, wherein R.sup.3 is selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, benzyl, substituted benzyl, phenacyl, phthalimidomethyl, .beta.-methylthioethyl, and 4-picolylor acid addition salts of such peptides, may be produced by peptide synthesis methods known per se.