Totalsynthese von Humaninsulin. IV. Beschreibung der Endstufen

Abstract

Total synthesis of human insulin. IV. Description of the final steps. SummaryRecently a preliminary account was given of a new synthetic pathway leading to human insulin. In the present report the last steps of this synthesis -i.e. as from the unsymmetrical cystine derivative I -are described in detail. I contains the sequences A(14-21) and B(17-30), linked by the disulfide bridge A20-B19. These last steps are : 1) selective removal by pH-controlled acidolysis in trifluoroethanol of N(K)-Trt from leucine B17, 2) completion of the B-chain by coupling with the fragment B(l-l6), 3) selective removal by trifluoroethanol of N(cr)-Bpoc at tyrosine A14, 4) completion of the A-chain by coupling with the cyclic fragment A (1-1 3), 5) removal of the acid labile protecting groups, and 6) formation of the disulfide bond A7-B7 from the two S-acetamido-protected cysteine residues by treatment with iodine.As judged by the composition of the reaction mixture the closure of the 85-membered ring proceeds with a cyclization yield of over 70%. From the last step in the synthesis two products were obtained after extensive purification by counter-current distribution: pure human insulin in a yield of 50% and its [D-tyrosine B16]Isomer in a yield of 25%. Although the partial racemization of tyrosine B16 occurred during coupling with sequence B( 1-16), the [D-tyrosine B 161-stereoisomer could only be separated at the endproduct stage.The available evidence indicates that the ease of formation of the disulfide bond A7-B7 does not depend on the precursor molecule already having an insulin-like conformation.Vorlaufige Mitteilung siehe [l].

The Prothoracicotropic Hormone Bombyxin has Specific Receptors on Insect Ovarian Cells

“…After 24 h at 37"C, the peptide was first purified by gel filtration on Sephadex G-50-sf in 1 M acetic acid followed by preparative HPLC (yield 20.5 mg, 26.5 %). The third disulfide bond was formed by oxidative removal of the Acm groups with iodine using the method of Sieber et al [18]. Acm-protected bombyxin (20.5 mg) dissolved in 20.5 ml 50% acetic acid was added to a stirring solution of 5.6 ml acetic acid, 6.9 ml 50 mM iodine in acetic acid, and 45 pl 6 M HCI.…”

Insulin structure and function

“…A fundamentally new approach pioneered by Sieber and coworkers [17][18][19] specifically addressed the low disulfide combination yield (Figure 2). They employed a stepwise assembly of the disulfides with initial assembly of the Cys A20-CysB19 linked heterodimer fragment A(14-21):B (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30).…”

“…The main limitations of this synthetic approach were the complicated protecting group scheme as well as the observed racemization in the formation of the B16-17 peptide bond. 19 This approach, however, was sufficiently versatile to permit synthesis of a series of analogs at milligram scale. 20,21 Of particular importance was the synthesis of two nonnative monomeric disulfide isomers: [CysA7-CysA11, CysA6-CysB7] and [CysA6-CysA7, CysA11-CysB7] human insulin where the native C-terminal disulfide is maintained.…”

The Chemical Synthesis of Rat Relaxin and the Unexpectedly High Potency of the Synthetic Hormone in the Mouse

“…The rat relaxin intermediate contains Acm-, N(in)formyl-and S-sulfoxide-protecting groups and was obtained in yields of 10.1 mg (1.3 pmol) for rat relaxin, 8.3 mg (1.1 pmol) for [B14D]rat relaxin and 11.1 mg (1.5 pmol) for [B14D, BISL, B16VIrat relaxin. The third disulfide bond was synthesized by direct oxidation of the Cys(Acm) group with iodine in aqueous acetic acid following the protocol of Sieber et al [21]. After HPLC purification, rat relaxin, protected in the side chains of tryptophan and methionine, was obtained at a yield of 2.71 mg (0.37 pmol).…”