Improvement to the esterification procedure used in solid phase peptide synthesis

beta-endorphin: synthesis and morphine-like activity of analogs with D-amino acid residues in positions 1, 2, 4, and 5

The solid-phase syntheses of [D-Tyr1]-, [D-Ala2]-, [D-Phe4]- and [D-Met5]-beta c-endorphins are described. A comparison of certain methods of purification and criteria of homogeneity is made with the use of these compounds. Bioassay of these synthetic analogs both in vitro and in vivo show that [D-Ala2]-beta c-endorphin possesses significant opiate activity whereas the other analogs have minimal activity.

Side reactions in solid-phase peptide synthesis and their applications

Side reactions in peptide synthesis indicate steps needing improvement as well as opportunities for structural diversification in combinatorial design. Among the side reactions observed in this study, transesterification of Boc-Glu(OBzl) occurred in TMAH-catalyzed resin attachment, leading to Boc-DKKREE(OMe) in solid-phase synthesis of Boc-DKKREE. Acetylation of Boc-Arg(NO2)-resin occurred during resin capping with Ac2O/Et3N, leading to GPR (Ac) in GPR synthesis. His- and Lys-modification occurred during GHRPLDKKREE cleavage from resin by Pd(OAc)2-catalyzed hydrogenation in DMF. To verify these side reactions, model experiments were performed, which indicated rapid transesterification of Boc-Glu(OBzl) in methyl, isopropyl, or tert-butyl alcohol into the corresponding ester by TMAH, but studies of acetylation showed that both Boc-Arg(NO2) and Boc-Arg(Tos) were stable to Ac-Im treatment, but were modified by Ac2O/Et3N. Since transfer hydrogenation of Boc-His(Bzl) and Boc-Lys(Z) in HCOOH or ammonium formate did not generate the formylated side-products of catalytic hydrogenation, DMF and not its decomposed product, HCOOH, appeared involved in side-chain modification. Elimination of the side reactions, by using Cs-derived Boc-Glu(OBzl)-resin for peptide synthesis and catalytic hydrogenation in NMP-HOPr for peptide cleavage, increased the GHRPLDKKREE yield by 1/3. On the other hand, the side reactions provided modified peptides, whose bioassays revealed different importance of the modified side-chains.

Synthesis and biological activities of [beta-Malyl1]- and [beta-Malyl1, Leu8]-angiotensin II analogues

The synthesis of [beta-Malyl1]- and [beta-Malyl1, Leu8]-angiotensin II using a solid phase procedure is reported. The replacement of the N-terminal amino group of aspartic acid by a hydroxyl group gives analogues with lower affinity than [Asn1]- and [Asn1, Leu8]-AII. However, the isoster [beta-Malyl1]-AII shows higher potency than [Asn1]-AII and this may be due to metabolic or enzymatic resistance.

Synthesis of [1-Aib]-angiotensin II, an analogue with higher potency than [1-Asn,5-Val]-angiotensin II

[1-Aib]-angiotensin II was synthesized by Merrifield's solid-phase procedure. The analogue, tested on rabbit aorta strips, showed intrinsic activity alpha E = 1, and when tested on rat blood pressure it gave a pD2 of 8.06; a 3.2 +/- 1.3-fold higher potency than the Ciba-Hypertensin standard.

Insulin-potentiating action of human growth hormone. Synthesis and activity of N-terminal fragments

Four peptides from the N-terminal region of human growth hormone have been synthesized by the solid-phase method: hGH(6-13), hGH(7-13), hGH(8-13) and hGH(9-13). Although these peptides contain the sensitive -Asp-Asn-sequence, apparently homogeneous products were obtained by synthesis on polystyrene resin, cleavage by hydrogen fluoride and purification by ion-exchange chromatography. The insulin-potentiating activity of these peptides is reported. The data indicates that extension of hGH(9-13) at its N-terminus is required for in vitro activity.

Synthesis and pharmacological properties of [1-N4-dimethyl-asparagine]-angiotensin II

[1-N4-Dimethyl-asparagine]-angiotensin II was synthesized by Merrifield's solid-phase procedure. The analogue gave rat blood pressure about 70% relative potency to Hypertension (Ciba). Rabbit aorta strips gave intrinsic activity alpha E = 1, a PD2 of 6.92 +/- 0.09 and an affinity relative to [Asn1]-angiotensin II of 6.5%.

beta-endorphin: synthesis and biological activity of shortened peptide chains

Three analogs of beta-endorphin have been synthesized by the solid-phase method: betac-endorphin-(1--5)-(28--31), betac-endorphin-(6--31) and betah-endorphin-(1--5)-(16--31). The analgesic activities of these synthetic peptides relative to that of the parent molecule are reported. All three peptides at high doses exhibit either no or much weaker analgesic activity than beta-endorphin. These data suggest that the entire beta-endorphin molecule is necessary for full in vivo analgesic activity.

Synthesis of a pentekontapeptide with high lipolytic activity corresponding to the carboxyl-terminal fifty amino acids of ovine beta-lipotropin

The synthesis of a peptide, composed of fifty amino-acid residues, corresponding to positions 42-91 in ovine beta-lipotropin has been accomplished by the solidphase method. The preformed symmetrical anhydride and active ester coupling methods were used exclusively. The synthetic product was purified by gel filtration, carboxymethylcellulose chromatography, and partition chromatography on Sephadex G-50. Its lipolytic activity in isolated rabbit fat cells was about six times that of beta-lipotropin on a weight basis.