Synthesis of Cypridina Luciferin and Related Compounds. I. : Synthesis of 2-Amino-5- (3-indolyl) -pyrazine

Abstract

To confirm the sutructure of Cypridina luciferin, synthesis of 2-amino-5- (3-indolyl) -pyrazine (XXI) was carried out by condensation of 3-indolylglyoxal and α-aminoacetamidine. We confirmed that the indolyl group in XXI is substituted at 5 and not at 6 position of the pyrazine ring in comparing the nuclear magnetic resonance spectrum of XXI with that of authentic 2-amino-5-phenylpyrazine (IX) obtained by condensation of phenylglyoxal aldoxime and aminoacetonitrile followed by reduction. IX was also synthesized from phenylglyoxal and α-aminoacetamidine. Ultraviolet spectral behavior of the pyrazine (XXI) is nearly identical with that of etioluciferin obtained from natural luciferin, indicating that both XXI and etioluciferin have the same chromophore.