Natural pigments containing four pyrrole rings joined by one-carbon units linking position 2 of one pyrrole ring to position 5 of the next. porphyrins are macrocyclic tetrapyrroles. E.g. bilin (a linear tetrapyrrole).
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Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1371 (https://doi.org/10.1351/pac199567081307)
See also:
White Book, 2nd ed., p. 279 (https://iupac.qmul.ac.uk/bibliog/white.html)