(1R)‐ and (1S)‐5‐demethyl‐8,16‐methanobacteriorhodopsin and its properties. The synthesis and spectroscopy of 5‐demethyl‐8,16‐methanoretinal in optically active and isotopic forms

Abstract

(All-E)-5-demethyl-8,16-methanoretinal was prepared in both optical antipodes (1R and 1S), as well as in their 9-Z and 13-Z forms. The interaction of the 1R and 1S forms with bacterioopsin shows that there is a clear chiral recognition on the formation of the bacteriorhodopsin analogues, reflected in the rate of binding and ϵ_max values. The two bacteriorhodopsins with optically active chromophores have an identical λ_max value and show the same efficiency of the light-driven proton pump. The absence of the 5-methyl group leads to a 50% lower proton-pump efficiency than the native system. In addition, for the racemic 5-demethyl-8,16-methanoretinal, the 5-²H, 7-²H, 5,7-²H₂ and 5,7,16a,16a-²H₄ isotopomers in the various isomeric forms all-E, 9-Z and 13-Z were also prepared.