J . Med. Chem. 1982,25, 795-801 ethylacetic anhydride by general procedure C: NMR (methanol-d,) 6 0.76-1.0 (m, 24 H), 1.22-1.70 [m, 13 H includes 6 1.30 (d), J N 7 Hz], 2.0-2.2 (m, 2 H), 2.31 (d, 2 H, J N 7 Hz), 3.89 (br m, 1 H), 3.98 (m, 1 H), 4.14 (d, 1 H, J E 7 Hz), 4.24 (9, 1 H, J H 7 Hz). N - (tert -Butoxycarbonyl)-~-valyl-L-valyl-4( S )-amino-3(S)-hydroxy-6-methylheptanoyl-~-alanyl Isoamylamide (9). The title compound wm prepared from HCl.Val-(S,S)-Sta-Ala-Iaa and the symmetrical anhydride of Boc-L-Val-OH by general procedure C: NMR (methanol-d,) 6 0.78-1.10 (m, 24 H), 1.24-1.78 [m, 18 H, includes 6 1.441, 1.87-2.20 (m, 2 H), 2.33 (d, 2 H, J = 7 Hz), 3.78-4.38 (m, 5 H). N - (tert -Butoxycarbonyl)-~-valyl-L-valyl-4( S)-amino-3(S)-hydroxy-6-methylheptanoyl-~-alanyl Isoamylamide (10). The title compound was prepared as described for 9 starting with Boc-D-Val-OH: NMR (methanol-d,) 6 0.80-1.02 (m, 24 H), 1.25-1.47 [m, 16 H, includes 6 1.431, 1.50-1.66 (m, 2 H), 1.95-2.22
795
(m, 2 H), 2.31 (d, 2 H, J 7 Hz), 3.85-4.02 (m, 3 H), 4.33 (d, 1 H , J N 7.5 Hz), 4.23 (4,1 H, J E 7 Hz). N-Isovaleryl-~-valyl-~-valyl-4( S)-amino-3(S)-hydroxy-6methylheptanoyl-L-alanyl Isoamylamide (1 1). The title compound was prepared from HC1-Val-Val-(S,S)-Sta-Ala-Iaa and isovaleric anhydride by general procedure C: NMR (methanol-d,) 6 0.75-1.0 (m, 30 H), 1.23-1.43 [m, 7 H, includes 6 1.30 (d), J 7 Hz], 1.49-1.68 (m, 3 H), 1.95-2.15 (m, 4 H), 2.31 (d, 2 H, J 7 Hz), 3.89 (broad, 1 H), 3.99 (m, 1 H), 4.14 (m, 2 H), 4.25 (9, 1 H, J N 7 Hz).
Acknowledgment. This work was supported in part by grants from the National Institutes of Health (AM 20100) and Merck Sharp & Dohme. We thank Dr. Paul G. Schmidt for 270-MHz NMR spectra of the inhibitors. We thank Dr. R. Bott for the preliminary X-ray data of the R. chinensis pepsin-pepstatin complex.
Synthesis and Biological Activity of Some Very Hydrophobic Superagonist Analogues of Luteinizing Hormone-Releasing Hormone1 John J. Nestor, Jr,,*it Teresa L. H o , ~Richard A. Simpson,? Bonnie L. Horner,? Gordon H. Jones,? Georgia I. McRae,* and Brian H. Vickeryt Institute of Organic Chemistry and Institute of Biological Sciences, Syntex Research, Palo Alto, California 94304. Received September 14, 1981 The effect of increased hydrophobicity at position 6 of luteinizing hormone-releasing hormone (LH-RH) has been investigated by the incorporation of a series of 15 very hydrophobic, unnatural D-amino acids at this position. The unnatural amino acids studied can be considered analogues of phenylalanine with carbocyclic aromatic side chains consisting of substituted phenyl (e.g., 2,4,6-trimethylphenyl,p-biphenyl) or polycyclic aromatic (e.g., naphthalene, anthracene) units. When enzymatic resolution (subtilisin Carlsberg) of the most hydrophobic amino acids failed, the racemic amino acids were incorporated, and the diastereomeric LH-RH analogues were resolved by preparative high-performance liquid chromatography. The analogues were synthesized by the solid-phase technique. All of [6the synthetic compounds were very potent LH-RH superagonists, but [6-(3-(2-naphthyl)-~-alanine)]LH-RH, (3-(2-naphthyl)-~-alanine),7-(N“-methylleucine)]LH-RH and [6-(3-(2,4,6-trimethylphenyl)-~-alanine)]LH-RH appear to be among the most potent LH-RH agonist analogues yet reported when tested in a rat estrus cyclicity suppression g; twice daily in =7 X assay designed to show the paradoxical antifertility effects of these compounds [ED50 saline]. These analogues are twice as potent as [ D - T ~ ~ ‘ , P ~ O N H E ~ ~ ] L inHthis -RH assay system (Le., -200 times the potency of LH-RH).
The isolation and determination of the structure of luteinizing hormone-releasing hormone (
