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 (cobalamines, corphyrins, corrins, vitamin B12 compounds)
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 (http://www.chem.qmul.ac.uk/iupac/bibliog/white.html)