Antagonists of luteinizing hormone releasing hormone with novel unnatural amino acids at position six

Expanding the Genetic Code

Although chemists can synthesize virtually any small organic molecule, our ability to rationally manipulate the structures of proteins is quite limited, despite their involvement in virtually every life process. For most proteins, modifications are largely restricted to substitutions among the common 20 amino acids. Herein we describe recent advances that make it possible to add new building blocks to the genetic codes of both prokaryotic and eukaryotic organisms. Over 30 novel amino acids have been genetically encoded in response to unique triplet and quadruplet codons including fluorescent, photoreactive, and redox-active amino acids, glycosylated amino acids, and amino acids with keto, azido, acetylenic, and heavy-atom-containing side chains. By removing the limitations imposed by the existing 20 amino acid code, it should be possible to generate proteins and perhaps entire organisms with new or enhanced properties.

New, highly active antagonists of LHRH with acylated lysine and p-aminophenylalanine in positions 5 and 6

A series of antagonists of the luteinizing hormone releasing hormone (LHRH) with substitutions in position 5 and/or 6 that included acylated lysine or p-aminophenylalanine were synthesized, characterized and tested for antiovulatory activity (AOA) in rats, and histamine releasing activity. Some of these antagonists were considerably more soluble at neutral pH than antagonists like Antide. Of 37 new antagonists, the best physico-chemical and biological properties were found for the following two analogs: NAcDNal-DCpa-DPal-Ser-PicLys-D(PicSar)Lys- Leu-ILys-Pro-DAlaNH2 (named Sartide) and NAcDNal-DCpa-DPal-Ser-Tyr-D(PicSar)Lys-Leu-IL ys-Pro-DAlaNH2. They are both soluble in water, inhibit ovulation completely at 0.5 microgram per rat, and have ED50 values for histamine release of about 30 micrograms/mL.