LH-RH antagonists: further analogs with ring-substituted aromatic residues

Synthesis and bioassay of LHRH-antagonists with N-Ac-D-O-phenyltyrosine and N-Ac-D-3-(2-dibenzofuranyl)alanine in position 1

N-Ac-D-O-phenyltyrosine was synthesized via the corresponding azlactone. Resolution of the DL methyl esters was achieved by Subtilisin Carlsberg. Treatment with palladium(II) acetate in trifluoroacetic acid converted N-Ac-D-O-phenyltyrosine into N-Ac-D-3-(2-dibenzofuranyl)alanine. These two amino acids were incorporated instead of N-Ac-D-2-Nal into position 1 of the LHRH-antagonist (N-Ac-D-2-Nal1, D-p-ClPhe2, D-3-Pal3, c-PzACAla5, D-PicLys6, ILys8,D-Ala10)-LHRH. The more rigid N-Ac-D-3-(2-dibenzofuranyl)alanine was structurally more effective than N-Ac-D-O-phenyltyrosine; the AOAs for the corresponding analogs were 82 and 38%, respectively, at 0.5 micrograms. Replacement of c-PzACAla in position 5 by O-phenyltyrosine significantly decreased potency.

Synthesis, resolution and characterization of ring substituted phenylalanines and tryptophans

Experimental protocols have been developed for the synthesis and resolution of numerous ring substituted phenylalanines and tryptophans in half mole quantities. Physical constants on these amino acids are given and their behavior on ion exchange supports (amino acid analyzer and post column ortho-phthalaldehyde derivatization) as well as that of some selected N-methylated amino acids is described. Those amino acids were then derivatized (N alpha-protection with the t-butyloxycarbonyl group) for solid phase peptide synthesis.

The role of N-acyl groups in the inhibitory activity of LH-RH analogues

Inhibitory analogues of luteinizing hormone-releasing hormone (LH-RH) were prepared with formyl-D-Trp1, acetyl-D-Trp1, valeryl-D-Trp1, tartaryl-D-Trp1, diacetyl-tartaryl-D-Trp1, acetyl-Gly1, and acetyl-Sar1 successively replacing the position one in the analogue [D-Trp1, D-p-Cl-Phe2, D-Trp3, D-Phe6, D-Ala10]-LH-RH. The formyl-D-Trp1 and acetyl-D-Trp1 analogues yielded 100% blockade of ovulation at the 10 micrograms dose; the others were less potent and inhibited ovulation at the 50 micrograms dose. The inhibitory potency seems to correlate with the polarity of the acyl group.

Facilitation of sexual receptivity in the rat by an ovulation-inhibiting analog of LHRH

An LHRH analog known to inhibit ovulation in the rat ([N-Ac-Phe1, D-p-Cl-Phe2, D-Trp3,6]-LHRH) was tested for its effects on sexual receptivity. The dose of 500 ng/rat was found in dose-response experiments to be most active and was further investigated for its behavioral effects in rats treated with either estrogen or estrogen plus progesterone. The analog significantly facilitated the behavior of rats in regimens producing low [estradiol benzoate (EB) (2 microgram)] and intermediate [EB (2 microgram) plus progesterone (2.5 mg)] levels of sexual behavior. In rats given regimens producing high behavioral scores [EB (5 microgram) plus progesterone (1 mg)], the peptide did not reduce mating behavior. In the same experiment, rats given EB (5 microgram) but not progesterone showed significantly higher scores after the LHRH analog only if they had been designated "responders" by a previous screening test with 1 microgram LHRH. These results demonstrate that in animals showing low, intermediate, or high levels of sexual behavior, the LHRH analog can affect mating behavior in a direction quite different from that exerted on pituitary reproductive functions.