Synthetic studies relevant to biosynthetic research on vitamin B ₁₂. Part 8. Synthesis of (±)-Faktor-I octamethyl ester

Several variations have been explored of the general synthesis of chlorins which uses a photochemical ring-closure of the macrocycle as the key step. This work leads to a synthesis of (±)-Faktor-I octamethyl ester, a chlorin which arises, in the free-acid form, by aromatisation of the mono-C-methylated intermediate on the biosynthetic pathway to vitamin B₁₂. This synthesis confirms the structure of Faktor-I and allows labelled samples to be prepared.