Pteridines, molecular structure

Studies on covalent hydration of N-heterocycles (67AG(E)919,76AHC(20)117) have revealed the diagnostic value of alkyl substituents in structural assignments due to their steric hindrance effects in addition reactions. C-Methyl substituents are therefore also considered as molecular probes to solve fine-structural problems in the pteridine field. The derivatives... 

The molecular features of covalent hydration are also present in the dihydroxy series, i.e., in pteridine-2,6-dione (30) and in pteridine-4,6-dione. The latter compound is hydrated only at the C(7)—N(8) double bond, whereas (30) forms two hydrated species, 7-hydroxy-7,8-dihydro- (29) and 4-hydroxy-3,4-dihydro-pteridin-2,6-dione (31) (equation 8). Structure (29) is thermodynamically the more stable substance (31) is formed more rapidly in solution but disappears slowly with time (63JCS5151). Insertion of a 4-methyl group greatly reduces the extent of 3,4- in favour of 7,8-hydration by a blocking effect . 

Nanostructures and nanochemistry are growth fields that have connections with the molecular scale and properties of DNA it is not surprising, therefore, that pteridines have been brought into research. Various structural types have been considered, for example, 246. 

Murakami and Shinkai have reported a calix[4]arene-based molecular receptor which changes from a closed form (intramolecular hydrogen bonds) to an open form (intermolecular hydrogen bonds with a pteridine guest) upon Na binding (Figure 88) [115]. Reduction of the fluorescence of the pteridine unit was observed in the presence of Na and the receptor, thereby providing evidence for the structure of the complex as shown. 

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