Yu. P. Shvachkin

ANTIOXIDATIVE ACTIVITY OF CYCLOHISTIDYLPROLINE

The antioxidative defense system is an important physiological system responsible for adapting living organisms to existence under aerobic conditions. This system protects vitally important compounds (lipids, proteins, DNA, RNA, etc.) against the damaging action of oxygen and of its activated forms [7]. Disturbances of the antioxidative defense system lead to severe pathological changes and to reactions of free radical oxidative destruction of membrane lipids and other biomolecules through the influence of activated forms of oxygen [7, 8]. The highest level of oxidative metabolism in vertebrates is characteristic of skeletal muscles and brain. These tissues also are distinguished by a relatively high content of various bioantioxidants, including ~-tocopherol (vitamin E), ascorbic acid (vitamin C), glutathione, and also carnosine and its related compounds [i, 9, i0].

Effect of the thyrotropin-releasing hormone analogue on an electrographic picture of sleep

Conclusions1.A-3, a TRH analogue, accelerates the time of onset of slow sleep and prolongs the duration of the deep slow sleep phase.2.The TRH analogue investigated decreases the inhibiting action of slow sleep on the respiration frequency.

Neuroendocrine effects of thyroliberin and its analogs

Conclusions1.TRH and A-1 shorten the duration of sleep.2.A-2 promoted an earlier onset of sleep and increased its individual phases.3.TRH and A-1 had marked antagonistic effects on nembutal toxicity.4.TRH analogs (A-1 and A-2) did not influence TTH secretion by the hypophysis.

[Sensitivity of hypothalamic neurons to beta-endomorphin, met-enkephalin, and thyroliberin].

: A study was made of susceptibility of hypothalamic neurons to beta-endorphine, thyroliberin and met-enkephalin applied microiontophoretically. The opioids were shown to exert a primarily unidirectional effect on the same neurons irrespective of the fact that the inhibitory action of beta-endorphine was more pronounced. The nalorphine-competitive antagonist of the opiates removed the met-enkephalin-induced inhibition. Unlike opioids, thyroliberin largely activated the test neurons. The possibility of neuropeptide participation in the control of gonadotropic function of the pituitary is discussed.

Synthesis of structural analogs of the 1–4 somatoliberin fragment

Amethod for the synthesis of new structural analogs of the 1–4 somatoliberin peptide sequence is described.

Synthesis of stereoisomer analogs of the amino end sequence of human growth hormone releasing factor

A new method has been developed for the synthesis of previously unreported stereoisomer analogs of the amino end sequence of the human growth hormone releasing factor.

Synthesis of structural analogs of the 16 – 19 somatoliberin sequence

Within the framework of investigations devoted to the peptide stimulation of insulin secretion, we have developed a method of synthesis and obtained a previously unreported peptide sequence representing a structural analog of the 16 – 19 somatoliberin sequence [1, 2]. In solving this task, we have studied three possible approaches. In the first case, we used carbonyldiimidazole as a condensing agent. The second method stipulated the formation of peptide bonds with the aid of 1,2-dihydroquinoline derivatives. In particular, we have studied the variants of peptide synthesis using N-ethyloxycarbonyl-2-ethyloxy1,2-dihydroquinoline (EEDQ) and N-isobutyloxycarbonyl2-isobutyloxy-1,2-dihydroquinoline (IIDQ). The third approach was based on the use of activated esters of N-protected amino acids. After experimental assessment and comparative analysis of possible variants, it was concluded that the most promising synthetic pathway to the target peptide is offered by the third approach. This method ensures a high yield of the target compounds, excludes undesired side reactions, allows effective control over racemization processes, and is less tedious than the other possible schemes. As a result, we have developed an effective method for the synthesis of previously unreported structural analogs of the 16 – 19 somatoliberin peptide sequence, which is a part of the amino end of somatoliberin. The distinguishing features of the proposed method are as follows: (i) Benzyl esters of amino acids and peptides play the role of amino components; (ii) Pentafluorophenyl esters of N-protected amino acids play the role of carboxy components; (iii) An acid-labile tert-butyloxycarbonyl protection is used for masking -amino acids in the carboxy components. (iv) p-Nitrophenyl esters are used in the case of -amides of dicarboxylic acids; (v) Stepwise construction of peptide chains in the C N direction. An important advantage of the proposed method is the possibility of using protected derivatives of trifunctional amino acids for the synthesis of hydrophobic analogs of somatoliberin. It was also established that the isolation of target compounds from the reaction mixtures is considerably simplified by conducting the condensation stage in DMF. In this case, the target peptides can be isolated in a crystalline state and purified by recrystallization. The structure of peptides obtained using the proposed scheme is uniquely determined by the scheme of synthesis. The synthetic analogs of the terminal region of somatoliberin can be obtained in an analytically pure form. The proposed method was used to obtain previously unreported peptides (I – VI), which are structural analogs of the 16 – 19 somatoliberin peptide sequence, representing a part of the amino end of somatoliberin. The initial compounds in our syntheses were L-alanine benzyl ester tosylate (VII), N-tert-butyloxycarbonylO-benzyl-L-serine (VIII), N-tert-butyloxycarbonyl-O-benzyl-L-leucine pentafluorophenyl ester (IX); and N-tert-butyloxycarbonyl-O-benzyl-L-glutamine p-nitrophenyl ester (X). Particular procedures involved in the synthesis of previously unreported peptides (I – VI) are described in detail below. The synthesis of the structural analogs of the 16 – 19 somatoliberin peptide sequence provides the necessary pre-

Synthesis of structural analogs of the 13 – 19 sequence of human growth hormone releasing factor

Development of the principles of synthesis of bioregulators responsible for the secretion of natural hormones in the organism is among currently important tasks. One particular basic problem consists in finding previously unknown peptide agents stimulating the secretion of insulin, a hormone playing a key role in the regulation of metabolic processes in higher mammals and humans. One possible approach to solving this problem is via the synthesis of peptide structures capable of participating in hormone – receptor interactions and enhancing insulin secretion by cells in Largenhans’ islets in the pancreas. A real pathway to such peptide stimulators of insulin secretion can be based on the synthesis of previously unknown structural analogs of the amino end region of somatoliberin, the hypothalamic releasing factor of human growth hormone [1, 2]. Our previous investigations showed that this R-factor is capable of indirectly influencing insulin biosynthesis and secretion by pancreatic islet cells. However, from the standpoint of pharmacology, a significant disadvantage of using natural somatoliberin as a bioregulator of insulin secretion is its relatively low activity and insufficient selectivity. In addition to weakly stimulating the secretion of insulin, natural somatoliberin enhances (to a much greater extent) production of growth hormone and activates the secretion of glucagon. For this reason, much better prospects in solving the problem under consideration can be related to the amino end region of somatoliberin. This conclusion agrees with the results of computer simulation of hormone – receptor interactions involved in the biosynthesis and secretion of insulin. In this context, we have undertaken a special investigation aimed at the development of a method for the synthesis of previously unknown structural analogs of the amino end region of somatoliberin, which can be of interest as potential stimulators of insulin secretion. After a series of preliminary experiments and a comparative analysis of the results, it was concluded that the most promising approach is that based on the use of activated esters of N-protected amino acids. This approach leads to a high yield of the target compounds, excludes undesired side reactions, allows effective control over the racemization processes, and is less tedious than the other possible schemes. As a result, we have developed an effective method for the synthesis of previously unreported structural analogs of the 13 – 19 somatoliberin peptide sequence, which is a part of the amino end of somatoliberin. Distinguishing features of the proposed method are as follows: (i) use of benzyl esters of oligopeptides as amino components; (ii) use of p-nitrophenyl or pentafluorophenyl esters of N-protected amino acids as carboxy components; (iii) use of an acid-labile tert-butyloxycarbonyl protection for masking -amino groups in the carboxy components; (iv) stepwise peptide synthesis in the C N direction. An important advantage of the proposed method is the possibility of using protected derivatives of trifunctional amino acids for the synthesis of hydrophobic analogs of somatoliberin. It was also established that the isolation of target compounds from the reaction mixtures is considerably simplified by conducting the condensation stage in DMF. In this case, the target peptides can be isolated in a crystalline state and purified by recrystallization. The structure of peptides obtained using the proposed scheme is uniquely determined by the scheme of synthesis. The synthetic analogs of the terminal region of somatoliberin can be obtained in an analytically pure form.

Synthesis of Structural Analogs of Thyroliberin with Single-Point Replacements of Amino Acid Residues

In the course of investigation of the quantitative relationship between chemical structure and biological activity of the peptide bioregulators of prolactin secretion, we have synthesized a series of previously unreported structural analogs of thyroliberin [1 – 3]. The new compounds (I and II) differ from the natural hormone by single-point replacements of L-histidine by L-alanine and L-phenylalanine, respectively:

Synthesis of a New Structural Analog of the Natural Thyrotropin-Releasing Hormone

Preliminary experiments showed that a promising approach to the synthesis of I is offered by a stepwise process in solution using a scheme based on peptide chain growth directed from an amino terminal acid residue toward the carboxy peptide chain end. Based on this scheme, we have developed an effective method for the synthesis of L-pyroglutamyl-L-seryl-L-norleucine amide (I). A distinguishing feature of the proposed method is the possibility of introducing a L-norleucine amide in the final stage of the peptide synthesis. It was established that the peptide bonds can be successfully formed using a combination of the activated ether method and the azide method. The initial compounds in our synthesis were L-pyroglutamic acid pentachlorophenyl ester (II), L-serine methyl ester hydrochloride (III), and L-norleucine amide (IV). Intermediate compounds included L-pyroglutamyl-L-serine methyl ester (V) and L-pyroglutamyl-L-serine hydrazide (VI). The structures of all intermediate peptides and the target peptide are uniquely determined by the scheme of synthesis. The final tripeptidamide I was obtained in an analytically pure form. Purity of the target product was confirmed by experimental chemical data and amino acid analysis. The proposed synthesis of pyroglutamyl-peptide I provides the prerequisites necessary to study biological activity of the new structural analog of TRH.