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■ Novel Synthetic Route of Coelenterazines -2-: Synthesis of Various Dehydrocoelenterazine Analogs

Nobuhiro Kondo, Masaki Kuse, Thumnoon Mutarapat, Nopporn Thasana, and Minoru Isobe*

*Laboratory of Organic Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan

Abstract

The novel synthetic route to introduce various substituents into 5-position of coelenteramine is described. Difficulties, however, are observed in the attempted synthesis of some analogs having labile functional groups. This is due to the strong acid conc. H₂SO₄ after Suzuki-Miyaura coupling, so that the route was limited only to the synthesis for aminopyrazines having acid-stable functional groups. In this report, we describe alternative success in the deprotection of N-tosyl-animopyrazine triflate before the cross coupling; thus, we obtained the aminopyrazine triflate in high yield. This compound enables us to synthesize various coelenterazine analogs. This triflate was proven to be so important intermediate that the versatile synthesis for coelenterazine and dehydrocoelenterazine analogs was established through Suzuki-Miyaura or Sonogashira coupling.