3 BACTERIORHODOPSINS WITH RING-DIDEMETHYLATED 6-S-LOCKED CHROMOPHORESAND THEIR PROPERTIES

Three novel, 6-s-locked rigidified retinals, racemic all-E 1,5-didemet hyl-8,16-methanoretinal, all-E 1,1-didemethyl-8,18-methanoretinal and all-E 8a,18-didehydro-1,1-didemethyl-8,18-methanoretinal were prepared in good yield in high purity on a 100-mg scale. For the preparation o f the key intermediate in the synthesis of 1,5-didemethyl-8,16-methano retinal, reductive cyanation of an unsaturated cyanohydrin to the corr esponding conjugated nitrile was accomplished using triethylsilane and trifluoroacetic acid. The three locked retinals interact with bacteri oopsin to form bacteriorhodopsin with about the same rate as the nativ e chromophore. This work proves that steric interaction of the 1,1-dim ethyl group in the chromophore is an important factor in binding to ba cterioopsin.