Nomenclature of Corrinoids

l.The corrinoids are a group of compounds containing four reduced pyrrole rings joined into a macrocyclic ring by links between their a -positions; three of these links are formed by one-carbon units (methylidyne radicals) and the other by a direct Ca-Ca bond.They include various B-12 vitamins, factors, and derivatives based upon the skeleton of corrin, C19H22N4 (structure 1).The atoms are numbered and the rings are lettered as shown in structure I.The numbering is thus the same as that of the porphyrin nucleus, number 20 being omitted to preserve the identity.Note.The name "corrin" was proposed by those who established its structure because it is the core of the vitamin B-12 molecule; the letters "co" of corrin arenot derived from the fact that vitamin B-12 contains cobalt.However, this does not apply to the "cob" terms below, all of which do contain "co" for cobalt.2. Some important corrinoids that are more unsaturated than corrin itself are derivatives of octadehydrocorrin.This has sometimes been called tetradehydrocorrin § because it has four additional double bonds.Although this could be indicated by the prefix "tetrakis(didehydro)", "octadehydro" is preferred.The octadehydrocorrin system lA has the trivial name corrole.3. Many important corrinoids have a regular pattern of substituents on the methylene carbon atoms of the reduced pyrrole rings and a cobalt atom in the center of the macrocyclic ring.The heptacarboxylic acid II is named cobyrinic acid.The carboxyl groups are designated by the locants a-g, as shown in 11.11 Cobyrinic a,b,c,d,e,ghexaamide, formerly sometimes referred to as Factor Vt •• is named cobyric acid.uSubstituents on the side chains may be designated by appropriate locants, e.g.7ß 1methylcobyrinic acid, if -CH(CH3)C02H replaces -CH2C02H at C-7ß of cobyrinic acid.4. The compound III (R=OH, R'=H), which is the amide formed by combination of cobyrinic acid with n-1-amino-2-propanol at position f, is named cobinic acid;l its hexaamide (111; R=H2N, R'=H) is named cobinamide.ll