Page 60 - Phytochemistry 2 (06-PG 605)
P. 60
Purine bases
https://www.sciencedirect.com/search?pub=The
%20Alkaloids%20Chemistry%20and%20Biology
Purines are derivatives of a heterocyclic nucleus consists of six
membered ring (pyrimidine) fused to a five membered ring
(imidazole).
The most important purine alkaloids are methylated derivatives
of xanthine nucleus. Caffeine is 1, 3, 7 trimethyl xanthine,
theobromine is 3, 7 dimethyl xanthine, theophylline is 1, 3 dimethyl
xanthine.
O R3 R1 R2 R3
N CH3 CH3 CH3
1 7 H CH3 CH3
R1 N CH3 CH3 H
N
O 3 Caffeine
N Theobromine
Theophylline
R2
The xanthine alkaloids are very weak bases, forming salts
with only very strong acids which can be easily hydrolyzed in
water. They do not give precipitate with Mayer’s reagent. They all
give Murexide positive test.
Caffeine
Properties
Caffeine occurs as a white powder or white glistening
needles. It is odourless sublimable (on heating) without
- ٥۹ -
