The coupling of arylboronic acids with 2,6-diamino-3,5-dibromo-1,4-pyrazine (6) gave 2,6-diamino-3,5-diaryl-1,4-pyrazines (7). The reaction of 7 with methyl glyoxal in aqueous EtOHHCl led to the N,N'-disubstituted products 8, instead of the expected bicyclic imidazolopyrazinones 1. The 2,6-bis[1-(ethoxycarbonyl)-ethylamino]-3,5-diaryl-1,4-pyrazines 8 are powerful inhibitors of the AAPH-induced linoleate peroxidation.Recently we became interested in the synthesis of imidazolopyrazinone derivatives 1 (Scheme 1) as potential antioxidants useful in medicinal chemistry for the design of drugs against injuries caused by oxidative stress. 1,2 Coelenterazine (CLZ), a naturally occurring imidazolopyrazinone of marine origin (1: R 1 = p-HO-Ph; R 2 = PhCH 2 ; R 3 = p-HO-PhCH 2 ; R 4 = H), is the luminescent substrate of enzymes (luciferases) producing light in the presence of oxygen. 3 Synthetic derivatives of coelenterazine can be obtained by condensing 2-amino-1,4-pyrazine precursors 2 with a-keto-aldehydes 3 (or the corresponding acetals) in aqueous acidic medium (Scheme 1). 4 Two routes have been exploited for the synthesis of aminopyrazines 2 equipped with natural or non-natural substituents R 1 , R 2 , and R 4 : (i) condensation of 1,2-propanedione-2-oxime derivatives with 2-amino-propionitrile compounds to form the substituted heterocycles; 5 (ii) functionalization of bromo-aminopyrazine derivatives via a Suzuki coupling reaction with boronic acid derivatives. 6 This last method was exemplified in our group for the preparation of a series of 3,5-diaryl-2-amino-1,4-pyrazines 2 (R 4 = H) and the related 6,8-diaryl-imidazolopyrazinones 1 (R 1 and R 2 = aryl; R 4 = H) which reveal to be powerful antioxidants. 1b
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