6.7- Diamino-5,6,7,8-tetrahydropteridine

Pteridine adds ammonia at low temperature to form 4-amino-3,4-dihydropteridine (246) which is transformed in a slower reaction into 6,7-diamino-5,6,7,8-tetrahydropteridine (247) (cf. similar adducts with water, 166 and 167). 

Pteridine and 2-chloropteridine were aminated by liquid ammonia (—40 °C) and potassium permanganate into the corresponding 4-aminopter-idines (86JHC473). Under these conditions no amino-dechlorination at C-2 was found. The regiospecificity of adduct formation is temperature dependent. At — 33 °C the C-4 adducts, i.e., the 4-amino-3,4-dihydro-2-R-pteridines (R = H, Cl), were formed as identified by NMR spectroscopy (Scheme 31). However, at temperatures up to 25 °C addition of ammonia takes place at positions C-6 and C-7, yielding the 2 1 a-adducts 6,7-diamino-5,6,7,8-tetrahydropteridines. Attempts to oxidize the C-6/C-7 diadduct into a 6,7-diaminopteridine were not successful (Scheme 31). 

Pteridine also adds ammonia at low temperature to form 4-amino-3,4-dihydropteridine (42) which is transformed in a slower reaction into 6,7-diamino-5,6,7,8-tetrahydropteridine (43) (Scheme 5). 2-Chloropteridine (36) shows the same behavior, whereas 2-chloro-4-phenylpteridine (37) and 2-methylthiopteridine (38) lead directly to the corresponding 6,7-diamino-5,6,7,8-tetrahydro derivatives (43) (Scheme 5). The 4-amino-3,4-dihydropteridines can easily be oxidized to the 4-aminopteridines <75RTC45>. Covalent hydrations with various 6,7-bis-trifluoromethyl-pteridine derivatives were studied showing that 6,7-bis-trifluoromethylpteridine (40) itself and the cor-... 

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