Synthesis, Properties, and NAD+-NADH-Type Redox Ability of 14-Substituted 1,3-Dimethyl-5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium Tetrafluoroborates and Their Hydride Adducts

Abstract

A synthesis of 14-substituted 1,3-dimethyl-5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates 11a,b(+).BF4- was accomplished by the methylation of 5,10-methanocycloundeca[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dione derivatives with MeI and following anion-exchange reaction by treatment with 42% aq HBF(4). Compound 11b(+).BF4- was synthesized alternatively by the reaction of 1,6-methano[11]annulenylium tetrafluoroborate with 6-phenylamino-1,3-dimethyluracil and following oxidative cyclization reaction. Remarkable structural characteristics of 11a,b(+)were clarified on inspection of the UV-vis and NMR spectral data as well as X-ray crystal analyses. The stability of cations 11a,b(+)() is expressed by the pK(R+) values which were determined spectrophotometrically as 9.8 and 9.7, which are smaller by 1.4 and 1.2 pH units than those of the corresponding seven-membered ring cations, respectively; however, the values are larger by 3.6 and 3.5 pH units than that of the parent 1,6-methano[11]annulenylium ion (pK(R+) = 6.2). The feature is rationalized on the basis of the perturbation derived from the bond fixation of the parent cation and the electron-donating ability of pyrrolopyrimidine. The electrochemical reduction of 11a,b(+).BF4- exhibited reduction potential at -0.58 and -0.52 (V vs Ag/AgNO3) upon cyclic voltammetry (CV). Reaction of 11a(+).BF4- with hydride afforded mixures of the C13- and C11-adducts in a ratio with hydride afforded, on the other hand, the C13-adduct as a single product. In both cations, the methano-bridge seemed to control the nucleophilic attack to the C13 favorably with exo-selectivity. The photoinduced autorecycling oxidation reactions of 11a,b(+).BF4- toward some amines under aerobic conditions were carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) with the recycling number of 1.1 to 32.2. Furthermore, as an example of the NAD+-NADH models, the reduction of a pyruvate analogue and some carbonyl compounds with the hydride adducts of 11a,b+.BF4- was accomplished for the first time to give the corresponding alcohol derivatives.