Page 184 - 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

340 Heterocyclic Chemistry

O Luminol is a pyridazine that upon oxidation gives a
striking emission of light. Veronal is a synthetic barbi-
N
O + turate that acts as a sedative and hypnotic. However, the
OMe
O
berberine NH 2 O
OMe
HN
NH
NH O N O
D. Five- and Six-Membered Rings H
O
with Two or More Heteroatoms
luminol veronal
An important pyrazolone is the developing agent
“phenidone,” widely used in black-and-white photogra- pyrimidines are the most important class of compounds
phy. Histamine is an imidazole connected with many in this group; the nucleic acids (see next subsection) are
based on the pyrimidine ring. Other important nitrogen
O H 2 N
heterocycles whose derivatives occur in nature are pteri-
N
NH dine, alloxazine, and uric acid (a metabolic product).
N N
Ph H H H H
"phenidone" histamine N N N N O O N N
O
N NH HN N
pathological conditions, including allergies—hence the N N H
development of antihistamine drugs. Derivatives of the O O
pteridine alloxazine uric acid
biologically important thiamine (vitamin B 1 ) assist in de-
carboxylation and transketolase reactions by forming a
There are many dyes based on cationic six-membered
nucleophilic zwitterion based on the thiazolium ring.
heterocyclic rings, such as Meldola’s blue and methylene
NH 2 blue, a biological staning agent.
R 1 R 2
+ +
N N N
_
N S OH S R 3 N
N
conversion of thiamine into a biologically active zwitterion +
Me 2 N O Me 2 N S _ NMe 2
+ Cl
The sydnones are aromatic heterocyclic betaines that
Meldola's blue methylene blue
have been called “mesoionic.” They have found use as
antimalarial agents.
1. Nucleic Acids
Ph Ph Ph
+
N N N
+ Nucleotides comprise a D-ribose or 2-deoxy-D-ribose
N _ N _ N _
O O O O O O
+ sugar, which is linked by C-5 to a phosphate unit and

canonical forms of a sydnone by C-1 to a nitrogen of one of six heterocycles, of which
three are pyrimidines—uracil, cytosine, and thymine—
A well-known derivative of isothiazole is saccharin, 500 and three are purines—adenine, guanine, and hypoxan-
times sweeter than sugar. thine.
O
NH 2
N
+ 6
N NH 6
O N 7 5 O O 5' N N
N _ S N 1 P
O O O 8 RO O N
O OH 1'
N 4 N 2 4'
an antimalarial sydnone saccharin 9 H 3' 2'
3
HO OH
purine
The three parent monocyclic diazines are pyridazine, R = H adenosine 5'-monophosphate
pyrimidine, and pyrazine.
Adenosine 5 -monophosphate is a typical nucleotide; it

N
N
contains the heterocyclic adenine 6-aminopurine. The di-
N
N N N and triphosphates (ADP and ATP) play central roles in
pyridazine pyrimidine pyrazine biological phosphorylation.