Luteinizing hormone-releasing hormone analogs with increased anti-ovulatory activity

A series of LH-RH antagonist analogs has been developed in which inhibitory activities have been increased to a potentially clinically useful level. The new peptides, which are typified by N-acetyl-D-p-Cl-Phe^1,2, D-Trp³, D-Phe⁶,D-Ala¹⁰]-LH-RH and N-acetyl-D-Trp^1,3,D-p-Cl-Phe²,D-Phe⁶, D-Ala¹⁰]-LH-RH, most importantly contain new modification to positions 1, 2 and 10, and induce full blockade of ovulation at single doses as low as 10 μg per rat (50 μg/kg). Various ring substituents on D-Trp or D-Phe in position 1 or other D-amino acid replacements in position 10 did not significantly improve anti-ovulatory activity. Incorporation of N-Me-Leu in position 7 was slightly detrimental to activity.