A. Wada et al., RETINOIDS AND RELATED-COMPOUNDS .17. CONFORMATIONAL STUDY OF RETINOCHROME CHROMOPHORE - SYNTHESIS OF 8,18-ETHANORETINAL AND A NEW RETINOCHROME ANALOG, Journal of organic chemistry, 59(23), 1994, pp. 6922-6927
In order to investigate the chromophore conformation around the trimet
hylcyclohexene ring in retinochrome, (all-E)-8,18-ethanoretinal (2), i
n which C-8 and C-18 positions of retinal 1 was connected by an ethyle
ne 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 ops
in shift (2200 cm(-1)) is of the same order of magnitude as that of na
tive 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 b
ond in retinochrome might correspond to the allowable torsional angle
in 8,18-ethanoretinal (2).