Reduction of Pteridines with Complex Metal Hydrides

Reduction of Pteridines with Complex Metal Hydrides 

The pteridine ring system is composed of fused pyrazine and pyrimidine rings, either of which might be attacked by a complex metal hydride. The reaction of pteridine (145), 2,4-dichloropteridine (146), or 2,4-dimethoxypteridine (147) with lithium aluminum hydride was reported to occur with reduction of the pyrazine ring to give the 5,6,7,8-tetrahydropteridine (148-150, respectively).150 

The product of the reaction of sodium or potassium borohydride with substituted pteridines is highly sensitive to the location of the substituent. Thus, Albert and Matsuura151 reported the formation of 2-oxo-l,2,3,4-tetrahydropteridine (152) from the reaction of potassium borohydride with pteridin-2-one (151). This appears to be the only example of attack of the pyrimidine ring of pteridines by complex metal hydrides. The same dihydropteridine (152) was formed by reduction of 151 with hydrosulfite ion, and the structure of the product of the latter reaction was elegantly proved using deuterium 

Oxo-groups located at other positions on the pteridine ring were shown by Albert and Matsuura152 to affect the structure of the dihydropteridine formed. Thus, pteridin-4- and 6-ones and 2,6- and 4,6-diones were converted to the corresponding 7,8-dihydro-derivatives (153), whereas pteridin-7-one and 4,7-dione formed the corresponding 5,6-dihydro-derivatives (154) on reaction with potassium borohydride. 

The reaction of derivatives of 2-ethylamino-8-ethyl-7-pteridinone carboxylic acid (155) with sodium borohydride gave the corresponding 4,8-dihydropteridine153 (156). The original assignment of the 5,8-dihydro-structure153 was revised on the basis of NMR studies of the reduction products.154 

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X. Reduction of Pteridines with Complex Metal Hydrides. . 91... 

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