into the target cobyric acid required the introduction of the two missing methyl groups at the meso positions of the corrin chromophore between rings A/B and C/D, as well as the conversion of all peripheral carboxyl functions into their amide form, except the critical carboxyl at the ring-D f-side chain (see fig. 6). These steps were collaboratively explored in strictly parallel fashion in both laboratories, the Harvard group using material produced via the A/B approach, the ETH group such prepared by the photochemical A/D approach. The first decisive identification of a totally synthetic intermediate on the way to cobyric acid was carried out in February 1972 with a crystalline sample of totally synthetic dicyano-cobalt(III)-hexamethyl-cobyrinate-f-amide 3 (fig. 6), found to be identical in all data with a crystalline relay sample made from vitamin B12 by methanolysis to cobester 4, followed by partial ammonolysis and separation of the resulting mixture. At the time when Woodward announced the "Total Synthesis of Vitamin B12" at the IUPAC conference in New Delhi in February 1972, the totally synthetic sample of the f-amide was one that had been made at ETH by the photochemical A/D approach, while the first sample of synthetic cobyric acid, identified with natural cobyric acid, had been obtained at Harvard by partial synthesis from B12-derived f-amide relay material. Thus, the Woodward/Eschenmoser achievement around that time had been, strictly speaking, two formal total syntheses of cobyric acid, as well as two formal total syntheses of the vitamin. In the later course of 1972, two crystalline epimers of totally synthetic dicyano-cobalt(III)-hexamethyl-cobyrinate-f-amide 3, as well as two crystalline epimers of the totally synthetic f-nitrile, all prepared via both synthetic approaches, were stringently identified chromatographically and spectroscopically with the corresponding B12-derived substances. At Harvard, cobyric acid was then made also from totally synthetic f-amide 3 prepared via the A/B approach. Finally, in 1976 at Harvard, totally synthetic cobyric acid was converted into vitamin B12 via the pathway pioneered by . The publication record Over the almost 12 years it took the two groups to reach their goal, both Woodward and Eschenmoser periodically reported on the stage of the collaborative project in lectures, some of them appearing in print. Woodward discussed the A/B approach in lectures published in 1968, and 1971, culminating in the announcement of the "Total Synthesis of Vitamin B12" in New Delhi in February 1972 published in 1973. This publication, and lectures with the