corrinoids (cobalamines, corphyrins, corrins, vitamin B12 compounds)

Derivatives of the corrin nucleus, which contains four reduced or partly reduced pyrrole rings joined in a macrocycle by three C01350-1 groups and one direct carbon–carbon bond linking α positions.
PAC, 1995, 67, 1307 (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1328
See also:
White Book, p. 272