Synthesis and biological activity of new conformationally restricted analogues of pepstatin.

A new statine derivative, 3-hydroxy-4-amino-5-mercaptopentanoic acid; cysteinylstatine (CySta), was synthesized and used to prepare a series of conformationally restricted analogues of pepstatin (Iva-Val-Val-Sta-Ala-Sta) in which the conformational constraint was introduced via a bis-sulfide connecting the appropriately substituted residues in the P1 and the P3 inhibitor side chains. The precursor peptide, Iva-Cys-Val-CySta-Ala-Iaa, was synthesized and alkylated with a series of dibromoalkanes and alkenes to produce the cyclic structures. This strategy permitted the carbon atom spacing between the P1 and the P3 inhibitor side chains to be systematically varied so as to produce inhibitors with 15-, 16-, and 17-membered ring systems. Additional non-cyclic analogues were synthesized as controls by alkylating the bisthiol intermediates with methyl iodide. The inhibitory potency of the analogues were determined against porcine pepsin and penicillopepsin by using standard enzyme kinetic assays. The cyclic inhibitor were found to be potent inhibitors of both aspartic proteases; inhibitor that contained a trans-2-butene link between the two sulfur atoms was found to be the most potent inhibitor with a Ki less than 1 nM against pepsin and 3.94 nM against penicillopepsin. This series of compounds illustrates a new type of conformational restriction that can be used to probe for the bioactive conformation of peptides.     

Acylases in plasma of hamsters with experimental hepatitis

After the administration of D-galactosamine to golden Syrian hamsters, a rapid but short-lived increase in acylase I and cobalt-activated (AA-Co) activity was noted in the blood plasma, but not in the liver. In the plasma of control hamsters, only form 2 AA-Co was identified, but during experimental hepatitis, the appearance of form 1 was observed. Only form 2 hamster enzyme is strongly inhibited by alpha-hydroxyisocaproil-tyrosine and reacts with antihuman form 2 antibody.     

Effect of intestinal gamma-glutamyl transferase inhibitor on the amount of gamma-glutamyl metabolites in mouse.

Experimental mice fed a balanced rodent chow, called LSM fodder, had markedly lower gamma-glutamyl transferase activity in the epithelium of intestinal villi then control mice fed wheat. After oral administration of gamma-14C-glutamyglycine, oxidized 14C-glutathione or gamma-glutamyl-p-amino-benzoate the amounts of gamma-glutamyl substrates and their metabolites in intestines, livers and kidneys of experimental mice were significantly lower than those in control mice. L-serine simultaneously administered with gamma-14C-glutamylglycine reduced the radioactivity of gamma-glutamyl substances in organs of the control mice. No differences in organ radioactivity of experimental and control mice were observed when some uniformly labeled with 14C amino acids were given. The obtained results are not in aggreement with hypothesis on a role of gamma-glutamyl transferase in amino acid transport.     

Microwave‐assisted 18O labeling of Fmoc‐protected amino acids

Recently, there has been an increased interest in isotopical labeling of peptides. Although there are several techniques allowing for a complete labeling of all carboxyl groups in peptides, regioselective labeling would be beneficial in many situations. Such labeling requires the use of ¹⁸O‐labeled Fmoc amino acids. We have designed a method for such labeling that is an improvement on a technique proposed earlier. The new procedure is suitable for microscale synthesis and could be used in peptide and proteomics laboratories. Although for the majority of tested amino acids our method gives good labeling efficiency, it is time consuming. Therefore, we have decided to use microwave‐assisted procedure. This approach resulted in reduction of reaction time to 15 min and increased reaction efficiency. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.