Page 180 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry
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Encyclopedia of Physical Science and Technology EN007F-314 July 6, 2001 16:59
336 Heterocyclic Chemistry
The oxidative condensation of certain pyrroles can lead ligand. In this biologically active and important molecule,
directly to the porphyrin nucleus, as in the case of oc- it is unsurprising to find a further type of heterocycle: a
taethylporphyrin. ribose ring, one of the sugars based on a hydrogenated
furan ring.
Other examples of naturally occurring furans are vita-
min C (ascorbic acid), first isolated from orange juice in
COOEt NH N
1. KOH 1928, and furfural, the artificial oil of ants, from which the
NH 2. AcOH, ∆, air solvent tetrahydrofuran is made.
N HN
HO
NEt 2
O O
HO O CHO
octaethylporphyrin HO OH
ascorbic acid furfural
Heme, the coloring portion of hemoglobin, and the
chlorophylls, the green pigments of plants, are both
Manyimportantindolesarefoundinnature:tryptamine,
porphyrins.
the parent of the essential amino acid tryptophan; the
powerful vasoconstrictor serotonin; and the powerful hal-
lucinogen lysergic acid diethylamide (LSD) are a few
N N N N examples.
Fe Mg
N N N N NH 2 HO NH 2
N N
H H
COOH O
HOOC C 20 H 39 OOC MeOOC tryptamine serotonin
heme chlorophyll a
O
H 2 NOC
CONH 2 Et 2 N
NMe
H
CONH 2
H 2 NOC
N CN N
Co +
H N
N N H
H 2 NOC lysergic acid diethylamide
Indoles have been used since ancient times; woad, the
CONH 2
O
NH coloring matter worn by Boudicca’s warriors, was an im-
pure form of indigotin (indigo) extracted from the plant
Indigofera tinctoria. Tyrian purple, the highly prized dye
_ O N
O P worn on the garments of emperors, is 6,6 -dibromoindigo,
O OH
O N and was extracted from the mollusc murex.
H
O
O H
N R
HO
cyanocobalamin
R N H
Vitamin B 12 (cyanocobalamin) is used to combat per- O
R = H indigo
nicious anemia; it was synthesized by Woodward and Es- R = Br Tyrian purple
chenmoser in brilliant and unparalleled sequences of over
30 reactions. The skeleton of vitamin B 12 is the corrin Thiophene itself is found in coal tar. Biotin, the human
macrocycle, differing from a porphyrin ring by having one growth factor vitamin H, contains a tetrahydrothiophene
less carbon atom in the linking of the four pyrrole rings. ring alpha-Lipoic acid, when enzyme-bound, is converted
Here, the nitrogen atoms of the pyrrole rings bind (act as into acetyl lipoate, which acetylates coenzyme A giving
ligands to) a central carbon atom. Moreover, a nitrogen acetyl coenzyme A, the biological building block that sup-
atom of a benzimidazole (heterocyclic) ring also acts as a plies two carbon atoms.