Heterocyclic Chemistry at a Glance

(やまだぃちぅ) #1

162 Heterocycles in Nature


Aromatic thiophenes play no part in animal metabolism, however they do occur in some plants, in association with
polyacetylenes with which they are biogenetically linked. Biotin (vitamin H) is a tetrahydrothiophene.


After the identifi cation of the thirteenth vitamin, vitamin B 12 , in 1948, there was a gap of 55 years before the fourteenth,
a pyrroloquinoline quinone (PQQ), previously known and named methoxatin as a redox enzyme cofactor in bacteria,
was shown, in 2003, to be a human dietary requirement.


Porphobilinogen and the ‘Pigments of Life’


Two other macrocycles crucial to all life are based on pyrroles. Chlorophyll a is the green pigment in plants that harvests
sunlight and so is at the commencement of the life cycle. Heme, the red pigment in blood, transports oxygen around
the body; the oxygen is attached to the iron as shown below.

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