Esterification of c-carboxyl with diazomethane afforded hexamethylester-f-nitrile E-41/HE-48. Treatment with Raney nickel in MeOH not only set free the two methyl groups at the meso positions, but also reductively opened the lactone ring to the free c-carboxyl group at ring B, producing the correct α-configuration at C-8. 1570-1571 What the two groups in fact accomplished thus were the common final steps of two different syntheses. 2:08:20-2:09:02 C-3 α-epimer (with the C-3 side chain below the plane of the corrin ring) reacted to a 5,15-disubstituted product E-38/H-45, the reaction thus amounting to a chemical separation of the C-3 epimers. E-17 in triethylphosphite (as both solvent and thiophile) afforded B-C-component E-18 as a (not separated) mixture of two epimers (regarding the configuration of the propionic side chain at ring B) in up to 80 % yield. 1414 Two HPLC fractions (Σ 5%) contained diastereomers with unnatural ligand helicity, as shown by inverse CD spectra. 24 This was crystallised and shown both as the α-cyano-β-aquo and the α-aquo-β-cyano form to be chromatographically and spectroscopically identical with the corresponding forms of natural cobyric acid. The final steps from the common corrinoid intermediate E-37/HE-44 to cobyric acid E-44/HE-51 were carried out by the two groups collaboratively and in parallel, the ETH group working with material produced by the A/D approach, and the Harvard group with that from the A/B approach.
The tasks in this end phase of the project were the regioselective introduction of methyl groups at the two meso positions C-5 and C-15 of E-37/HE-44, followed by conversion of all its peripheral carboxyl functions into primary amide groups, excepting that in side chain f at ring D, which had to end up as free carboxyl. Formulae in figs. 4 and 6 illustrate the atom, ring, and side chain enumeration in corrins: "Nomenclature of Corrinoids". The most efficient way of attaching the two rings D and A to the B-C-component E-18 was to convert E-18 directly into its thiolactam-thiolactone derivative E-20 and then to proceed by first coupling ring-D precursor E-29 to ring C, and then ring-A precursor E-31 to ring B, both by the sulfide contraction method. Attachment of ring-D precursor E-29 to the ring-C thiolactam in E-20 by sulfide contraction via alkylative coupling (t-BuOK in t-BuOH/THF, tris-(β-cyano-ethyl)-phosphin/CF3COOH in sulfolane) afforded the B/C/D-sesqui-corrinoid E-32. The conversion of bicyclic lactone-lactam E-18 into the corresponding thiolactone-thiolactam E-20 was brought about by heating with P2S5/4-methylpyridine in xylene at 130 °C; milder condition produced thiolactam-lactone E-19, used for coupling with the Harvard A-D-components. This was cre ated wi th the he lp of GSA Content G enerat or Dem oversion.
When treated with thiophenol, this produced the bis-phenylthio-derivative E-40/HE-47. E-35 produced E-37 in yields of 70-80% as an essentially dual mixture of mainly the 3α,8α,13α epimer, besides some 3α,8α,13β epimer. In the course of 1972, comprehensive identifications (HPLC, UV/VIS, IR, NMR, CD, mass spectra) of crystalline samples of totally synthetic intermediates with the corresponding compounds derived from vitamin B12 were carried out in both laboratories: individually compared and identified were the 3α,8α,13α and 3α,8α,13β neo-epimer of f-amide E-42/HE-49, as well as the corresponding pair of C-13-epimeric nitriles E-41/HE-48. Less than 1% of fractions with unnatural coil were formed (HPLC, UV/VIS, CD). 21 A crystalline sample of the 3α,8α,13α-epimer of dicyano-cobalt (III)-a,b,c,d,e,g-hexamethyl-cobyrinate-f-amide E-42/HE-49, isolated by HPLC, was the first totally synthetic intermediate to be chromatographically and spectroscopically identified with a relay sample made from vitamin B12. 1567-1568 In this final phase of the synthesis, HPLC again turned out to be absolutely indispensable for separation, isolation, characterization and, above all, identification of pure isomers of dicyano-cobalt(III)-complexes of totally as well as partially synthetic origin. These thorough identifications of the totally synthetic with partially synthetic materials mark the accomplishment of the two syntheses.
44-45 the solvent in which cobyric acid was to be identified, and where it exists as two easily equilibrating aquo-cyano complexes, epimeric regarding the position of the two non-identical axial Co ligands. The search for the reaction conditions for these attachments was greatly facilitated by exploratory work done on the two sulfide contraction steps in the A/B approach model study. 26-27,196-221 At Harvard, the transformation E-43/HE-50 → E-44/HE-51 was eventually carried out starting with f-amide that had been obtained by total synthesis via the A/B approach. Cholesterol is carried through the blood, packaged in LDL particles; LDL is responsible for depositing cholesterol in the walls of the arteries. Second, animal foods are not the best source because consuming them increases our levels of IGF-1 (a hormone consistently associated with increased cancer risk and tumor growth), TMAO (a substance that injures the lining of our blood vessels and promotes the formation of cholesterol plaques), as well as other unhealthy substances such as heme iron, which is associated with oxidative stress and the formation of free radicals.