Synthesis and Biological Evaluation of Two New Analogues of Gonadotropin Releasing Hormone (GnRH)D-alanine8 and D-alanine

Abstract

So far synthesis of Gonadotropin Releasing Hormone (GnRH) analogues reported in the literature has clarified some aspects of structural activity of the naturally released GnRH. As a part of continuing efforts for further understanding of this relationship, the present investigation was undertaken which involved synthesis and biological evaluation of two GnRH analogues, firstly, by replacement of the amino acid L-Argenine in the 8^th position at the backbone structure of the natural hormone by the amino acid D-Alanine; and secondly, by replacement of the amino acid L-Glycine in the 10^th position by D-Alanine also at the backbone structure of the nature hormone, to obtain the following analogues respectively:

PGlu-His-Trp-Ser-Tyr-Gly-Leu-DAla-Pro-Gly-NH₂ (Analogue I: D-Alanine⁸ GnRH),

PGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-DAla-NH₂ (Analogue II: D-Alanine¹⁰ GnRH), which were synthesized by applying conventional solution method. Peptides were purified by several recrystallization using appropriate solvent and proved to be homogenous. Conformity of the synthetic procedure was achieved by applying different physico-chemical analyses including Melting Point (mp), Thin Layer Chromatography (Tlc.), Infrared Spectroscopy (IR), Elemental Analysis (CHN), Amino Acid Analysis (AAA), and Nuclear Magnetic Resonance (H¹NMR).Preliminary biological activity of the two analogues was determined by testing their effects of parenteral administration on ascorbic acid depletion from the ovary of pseudopregnant mice and compared with that of natural GnRH hormone. Analogue II showed significant ascorbic acid depletion as compared to the native hormone while the percentage in ascorbic acid depletion after administration of analogue I were not significant as compared to the native hormone.

Key Words: Gonadotropine releasing hormone, Peptide synthesis, Biological activity of GnRH