Natural pigments containing a fundamental skeleton of four pyrrole nuclei united through the α-positions by four methine groups to form a macrocyclic structure (porphyrin is designated porphine in Chemical Abstracts indexes).
See also: corrinoids
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1360 (https://doi.org/10.1351/pac199567081307)
White Book, 2nd ed., p. 281 (https://www.qmul.ac.uk/bibliog/white.html)