Derivatives of the corrin nucleus, which contains four reduced or partly reduced pyrrole rings joined in a macrocycle by three
C01350-1.png groups and one direct carbon–carbon bond linking α positions.
C01350-2.png
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1328 (https://doi.org/10.1351/pac199567081307)
See also:
White Book, 2nd ed., p. 272 (https://iupac.qmul.ac.uk/bibliog/white.html)