Configurationally stable analogs of styrylxanthines as A(2A) adenosine receptor antagonists

Article abstract of DOI:10.1016/S0223-5234(97)88913-1

Configurationally stable analogs of the potent, A(2A)-selective adenosine receptor (AR) antagonist 3,7-dimethyl-1-propargyl-8-styrylxanthine (8-styryl-DMPX, 3) were synthesized and investigated in radioligand binding assays for affinity to the high-affinity A₁- and A(2A)-AR subtypes of rat brain. All derivatives prepared, including compounds in which the styryl double bond was replaced by a cyclopropane ring or a triple bond, or in which it was integrated into a (hetero) cyclic ring system, were less potent and less selective compared to the parent compound 3. The best compound of the present series was 8-(phenylethynyl)-DMPX (21), exhibiting a K(i) value at A(2A)-AR of 300 nM and a > 10-fold selectivity versus A₁-AR. In view of its configurational stability, 21 may be an interesting lend compound for the development of more potent A(2A) antagonists by introducing appropriate substituents in the phenyl ring. Based on conformational analysis of 8-styrylxanthine and 8-(2-naphthyl)xanthine derivatives, it is hypothesized that the bioactive conformation of (E)-8-styryl substituents with regard to the imidazole ring of the xanthine nucleus at A(2A)-AR may be nearly coplanar and cisoid, and may differ from the bioactive conformation of such xanthine derivatives at A₁-AR.