Bacteriopurpurin 1 (I) was obtained from the extracts of Rhodobacter sphaeroides, enriched with bacteriochlorophyll a, by treatment with KOH/n-propanol in the presence of air. Subsequent acidification of the propanol solution of (I) produced the propyl ester (II). Opening of the anhydride ring system of (II) with n-hexylamine led to a mixture of regioisomeric amido-acid compounds, which were further converted to the respective amido-esters (III) and (IV) upon treatment with diazomethane. Repeating several times the dissolution of this mixture in THF, followed by evaporation of the solvent, gave rise to the cyclic imide (V). The keto group of (V) was then reduced to alcohol (VI) employing NaBH4 in MeOH.
Alcohol (VI) was converted to alkyl bromide (VII) by means of a solution of HBr in HOAc. Subsequent displacement of the bromide ion of (VII) with n-heptanol in the presence of K2CO3 furnished the title heptyl ether. Alternatively, alcohol (VI) was dehydrated to the vinyl bacteriopurpurin (VIII) by a short reflux in ortho-dichlorobenzene. Then, addition of HBr to the vinyl group, followed by treatment with heptyl alcohol, afforded the target compound.