Page 169 - 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

Heterocyclic Chemistry 325

Piperine (L. piper = pepper) is a piperidine found in ton (rings A–D) with a perhydroindole nucleus (rings
black pepper. Aspergillic acid is an antibiotic found in E and F). Strychnine, the notorious poison, first isolated
Aspergillus flavus. Folic acid is a B vitamin widely from Strychnos ignatii in 1818, contains several fused het-
distributed in living matter. erocyclic rings; it was the subject of a brilliant synthesis
in the 1960s.
OH
H
N O N
E F H
C D N
N H
A B N H O
aspergillic acid H
HO
solanidine O strychnine
H
H 2 N N N
H
N N
N II. PHYSICAL PROPERTIES
H
O N COOH
folic acid O COOH Physical properties offer good criteria for the purity of
heterocycles, just as they do for other organic compounds.
More complex molecules frequently involve an array of The melting or boiling points were the characteristics for-
chiral centers. Riboflavin (vitamin B 2 ) is an isoalloxazine merly most frequently used, but optical spectra (based on
involved in nutrition; its richest natural source is yeast. absorption of light) and nuclear magnetic resonance spec-
tra have become increasingly used. As for very many or-
OH
ganiccompounds,heterocyclesdisplaypreciseandreadily
HO
OH reproducible physical properties.
OH
A. Melting and Boiling Points
N N O
NH Melting and boiling points of common heterocycles are
N
given in Tables III and IV. The boiling points of many
O
riboflavin of the heterocycles listed are substantially higher than
those of the analogous cycloalkanes. Many simple hete-
Other examples are 1-hydroxymethylquinolizidine, rocycles are mobile, pungent liquids at room temperature.
found in yellow lupin seeds, and thromboxane A 2 , an im- Because molecular weight is related to vapor density,
portant component in blood platelet aggregations. smaller molecules are, on the whole, more volatile than
OH larger ones. An example can be seen in the compari-
H COOH son of alkylfurans with alkylbenzenes, the latter analogs
O
being heavier by C 2 H 2 O =10 mass units; the furans boil
O
N at about 40 C lower than the corresponding benzenes.
◦
OH
1-hydroxymethylquinolizidine thromboxane A 2
TABLE III Boiling Points of Saturated Heterocycles and Cor-
◦
Structural elucidation of many natural products paves responding Carbocycles ( C at 1 atm)
the way for their synthesis; multistriatin was synthesized Number and Heteroatom type
and used to trap the male elm bark beetle, which carries Ring orientation of Saturated
the fungus causing Dutch elm disease. Many naturally oc- size heteroatoms NH O S cycloalkane
curring heterocycles, such as cocaine (isolated from cocoa
3 One 56 11 55 −34
leaves) and morphine (from the opium poppy), have im-
4 One 63 48 94 13
portant pharmacophysiological properties.
5 One 87 66 121 49
Me 6 One 106 88 141 80
N COOMe
6 Two (1,2) 165 a — — 80
6 Two (1,3) 150 106 — 80
OCOPh
6 Two (1,4) 145 101 200 80
cocaine
7 One 138 120 174 119
Exceedingly complex structures have invariably proved a
Corrected to atmospheric pressure by the method of Hass and
fascinating to the organic chemist. Solanidine, found in Newton (1970). In “Handbook of Chemistry and Physics,” 51st ed.
potato shoots, is a formal fusion of a steroid skele- (Weast, R. C., ed.), CRC, Cleveland, OH.