RES-701-2, a novel and selective endothelin type B receptor antagonist produced by Streptomyces sp. II. Determination of the primary structure.

Endothelins (ETs) are a family of potent vasoactive peptides found in at least three distinct isoforms: ET-1, ET-2, and ET-31}. Two major subtypes of endothelin receptors, termed ETAand ETB, have been identified in various target cells2). It is well known that ETs act on these G protein-coupled receptors and exert multiple pharmacological effects3). As the development of potent and selective endothelin receptor antagonists facilitates the understanding of endothelin4), the function of ETB receptors is yet to be fully elucidated. In a preceding paper, we elucidated the isolation, physico-chemical and biochemical properties, and structural determination of RES-701-1, a novel endothelin type B receptor antagonist5'6). In the course of further screening programs for ET receptor antagonists from culture broths of microorganisms, we discovered other structural related peptides, RES-701-2, -3 and -4 in the culture broth of Streptomyces sp.7). This paper describes the primary structure elucidation of RES-701 -2 including DL-amino acid analysis. FAB-massspectrometry analysis revealed that the molecular weight of RES-701-2 is 2059, which is 16 mass higher than RES-701-l6). The molecular formula of RES-701-2 was confirmed as C103H115N23O24 by high resolution-FAB-MS analysis (calcd: 2058.8503 for M + H, found: 2058.8496) and amino acid analysis (found: Asx3, Gly2, Hisl, Thrl, Alal, Prol, Tyr2, Phe2, Trp2 ). The