A novel class of heterocyclic aromatic amino acids based on the 3-(2-benzimidazolyl)alanine system has been generated by chiral synthesis from D- or L-aspartic acid. The use of variously substituted o-phenylenediamines for condensation with the beta-carboxyl function of alpha-benzyl N-(benzyloxycarbonyl)-D-aspartate has led to a series of amino acids of graded hydrophobicity with a steric bulk similar to that of tryptophan. In a similar fashion, we have prepared 3-(2-benzothiazolyl)-D-alanine from o-aminothiophenol and 3-(2-benzoxazolyl)-D-alanine from o-aminophenol. Incorporation of these amino acids into the 6-position of luteinizing hormone-releasing hormone (LH-RH) led to a series of very potent agonist analogues (up to 160 times LH-RH potency), active in doses ranging from 0.1 to 0.5 microgram by twice daily injection in a rat estrus cyclicity suppression assay designed to show the paradoxical antifertility effects of these compounds.

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 the synthetic compounds were very potent LH-RH superagonists, but [6-(3-(2-naphthyl)-D-alanine)]LH-RH, [6-(3-(2-naphthyl)-D-alanine), 7-(N alpha-methylleucine)]LH-RH and [6-(3-(2,4,6-trimethylphenyl)-D-alanine)]LH-RH appear to be among the most potent LH-RH agonist analogues yet reported when tested in a rat estrus cyclicity suppression assay designed to show the paradoxical antifertility effects of these compounds [ED50 approximately 7 x 10(-8) g; twice daily in saline]. These analogues are twice as potent as [D-Trp6,ProNHEt9]LH-RH in this assay system (i.e., approximately 200 times the potency of LH-RH).

A high incidence of tumor regression was observed in guinea pigs bearing transplantable, line-10 hepatocellular carcinomas when synthetic muramyl dipeptides combined with trehalose dimycolate in oil-in-water emulsions were injected directly into the tumors. These compounds are promising candidates to replace viable bacillus Calmette-Guérin in cancer immunotherapy in humans and animals.

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Im Peptid Glu‐His‐Trp‐Ser‐Tyr‐Gly‐ Leu‐Arg‐Pro‐Gly‐NHQ (= LH‐RH) wird die 6‐Position durch die lipophilen D‐Amino‐ säuren (I) und (V) ersetzt.