Pteridine. Teil XCIV . Synthese und Eigenschaften von 5,6‐Dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridinen: Kovalente intramolekulare Addukte

Pteridines: Synthesis and Characteristics of 5,6‐Dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridines: Covalent Intramolecular Adducts Various 5,6‐diaminopyrimidines ( 1, 15, 24, 33 ) were condensed with the phenylhydrazones of L ‐( 2 ) and D ‐arabinose ( 3 ) in acidic medium under N 2 to give formal 5,6‐dihydro‐6‐(1,2,3‐trihydroxypropyl)pteridines (see, e.g. , 4 and 5 ), the latter turned out to exist preferentially as intramolecular adducts, the hexahydropyrano‐[3,2‐ g ]pteridines 6, 7, 16, 17, 25, 26 , and 34 , formed subsequently by addition of the terminal OH group of the side‐chain to the C(7)N(8) bond of the pteridine moiety. Spectroscopically, the isomeric hexahydrofuro‐[3,2‐ g ]pteridines 10,11,18,19 , and 35 were also detected as minor components in the equilibrium mixtures. In the 4‐amino‐2‐(methylthio)pteridine series, crystallization of 6 and 7 led to the stereochemically pure (3 S ,4 R ,4a R , 10a S )‐6‐amino‐3,4,4a,5,10,10a‐hexahydro‐8‐(methylthio)‐2 H ‐pyrano[3,2‐ g ]pteridine‐3,4‐diol ( 8 ) and its corresponding enantiomer 9 , respectively Structure 8 was proven by X‐ray analysis. Acylation of the hexahydropyrano[3,2‐ g ]pteridines yielded the more stable tri‐, tetra‐, and pentaacetyl derivatives 12–14, 20–23, 27–32 , and 37–39 which were characterized and of which the absolute and relative configurations were determined ( 1 H‐ and 13 C–NMR and UV spectra, chiroptical measurements, elemental analyses).