摘要:
In order to investigate the chromophore conformation around the trimethylcyclohexene ring in retinochrome, (all-E)-8,18-ethanoretinal (2), in which C-8 and C-18 positions of retinal 1 was connected by an ethylene group, was synthesized via the Dieckmann condensation of diester 6 from 2,2-dimethylcyclohexanone 7. This analog 2 was incorporated into aporetinochrome, forming a pigment with lambda(max) at 498 nm. Its opsin shift (2200 cm(-1)) is of the same order of magnitude as that of native retinochrome (2400 cm(-1)), suggesting that the conformations of both chromophores are fairly similar in the protein. In addition, MMX calculations indicate that the torsional angle around the 6-7 single bond in retinochrome might correspond to the allowable torsional angle in 8,18-ethanoretinal (2).