H-D-Leu-Thr-Arg-PNA

This review documents my research for the past 45 years in peptide chemistry. Initially, in order to study the structure-activity relationships of active center of alpha- and beta-melanocyte stimulating hormones (H-His-Phe-Arg-Trp-Gly-OH), we employed D-amino acids. That approach yielded first published report in 1965 of antagonists containing D-amino acids. Monkey beta-melanocyte stimulating hormone (beta-MSH), an 18 amino acid peptide stimulated pigment cells. We synthesized beta-MSH and fragments thereof, and studied in detail structure-activity relationships. A major and valuable result revealed that the C-terminal pentadecapeptide of beta-MSH exhibited higher MSH activity than the parent hormone providing a new question; namely, what was the role of the N-terminal tripeptide? In order to identify the novel enzyme, spleen fibrinolytic proteinase (SFP), I developed a specific chromogenic substrate, Suc-Ala-Tyr-Leu-Val-pNA, and a specific inhibitor, Suc-Tyr-D-Leu-D-Val-pNA, once again employing my D-amino acid strategy. SFP was purified by affinity chromatography using Suc-Tyr-D-Leu-D-Val-pNA as the bound ligand. The success of this approach provided me the incentive to develop a variety of potential drugs. Thus, I prepared a specific plasmin inhibitor (YO-2) and a plasma kallikrein inhibitor (PKSI-527). Next, my research developed novel opioid receptor specific opioid agonists and antagonists based on 2',6'-dimethyl-L-tyrosine (Dmt) dimers coupled with unique pyrazinone ring as a spacer. They exhibited potent oral antinociceptive activity acting through the mu-opioid receptor. Potent mu-receptor agonists (H-Dmt-Pro-Phe/Trp- Phe-NH(2)) were transformed into highly selective mu-receptor antagonists (N-allyl-Dmt-Pro-Phe/Trp-Phe-NH(2)), which reversed ethanol-induced increases in GABAergic neurotransmission, suggesting the possibility that they may emerge as candidates for the treatment of ethanol addiction.

We synthesized short chromogenic peptidyl-Arg-p-nitroanilides containing either (Galbeta)Ser or (Glcalpha,beta)Tyr at P2 or P3 sites as well as O-acetylated sugar moieties and studied their hydrolysis by bovine trypsin, papain, human tissue kallikrein and rat tonin. For comparison, the susceptibility to these enzymes of Acetyl-X-Arg-pNa and Acetyl-X-Phe-Arg-pNa series, in which X was Ala, Phe, Gln and Asn were examined. We also synthesized internally quenched fluorescent peptides with the amino acid sequence Phe8-His-Leu-Val-Ile-His-Asn14 of human angiotensinogen, in which [GlcNAcbeta]Asn was introduced before Phe8 and/or after His13 and ortho-aminobenzoic acid (Abz) and N-[2-, 4-dinitrophenyl]-ethylenediamine (EDDnp) were attached at N- and C-terminal ends as a donor/receptor fluorescent pair. These peptides were examined as substrates for human renin, human cathepsin D and porcine pepsin. The chromogenic substrates with hydrophilic sugar moiety increased their susceptibility to trypsin, tissue kallikrein and rat tonin. For papain, the effect of sugar depends on its position in the substrate, namely, at P3 it is unfavorable, in contrast to the P2 position that resulted in increasing affinity, as demonstrated by the higher inhibitory activity of Ac-(Gal3)Ser-Arg-pNa in comparison to Ac-Ser-Arg-pNa, and by the hydrolysis of Ac-(Glcalpha,beta)Tyr-Arg-pNa. On the other hand, the acetylation of sugar hydroxyl groups improved hydrolysis of the susceptible peptides to all enzymes, except tonin. The P'4 glycosylated peptide [Abz-F-H-L-V-I-H-(GIcNAcbeta)N-E-EDDnp], that corresponds to one of the natural glycosylation sites of angiotensinogen, was shown to be the only glycosylated substrate susceptible to human renin, and was hydrolysed with lower K(m) and higher k(cat) values than the same peptide without the sugar moiety. Human cathepsin D and porcine pepsin are more tolerant to substrate glycosylation, hydrolysing both the P'4 and P4 glycosylated substrates.