Chemistry Reference
In-Depth Information
B6
Pyridoxine
B7
Biotin
B9
Folate
B12
Cobalamin
13.2.
Thiamine (Vitamin B1)
Thiamine is a water-soluble vitamin, is unstable and thus loses its biological
activity in alkaline solutions (pH
>
7) as well as in the presence of oxidants
and radiation. The chemical name of thiamine is 3-[(4-amino-2-methyl-5-
pyrimidinyl)methyl]-5-(2-hydroxyethyl)-4-methylthiazolium; its co-enzyme
form is thiaminepyrophosphate (TPP; Figure 13.1).
In pharmaceutical and other preparations, thiamine is used in the form
of water-soluble thiazolium salts (thiamine chloride hydrochloride, thiamine
mononitrate); there are also synthetic lipophilic derivatives (the so-called
allithiamins). The latter can pass through biological membranes more easily
and in an almost dose-related manner, thus offering a possibility to develop
thiamine stores by supplementation, which under normal circumstances are
low and sufficient for only 4-10 days (Biesalski and Back, 2002a).
In the presence of oxidizing agents and in strongly alkaline solutions,
thiamine is converted to thiochrome, a fluorescent substance used to deter-
mine the thiamine content of feeds, foods or pharmaceutical preparations
(Alonso et al., 2006).
13.2.1.
Thiamine Function
A number of enzymes involved in intermediary metabolism and playing
a role in the oxidative decarboxylation of alpha-keto acids require TPP as co-
enzyme (pyruvate-dehydrogenase complex; alpha-ketoglutarate dehydrogen-
ase complex; branched chain alpha-keto acid dehydrogenase complex). Thus,
metabolites from carbohydrate metabolism and keto analogues from amino
H
2
C
H
2
CH
3
CH
3
C
N
+
N
+
N
N
H
2
S
S
N
N
H
3
C
H
3
C
C
C
OPP
C
H
2
CH
2
OH
NH
2
NH
2
H
2
Pyrimidine ring
Thiazole ring
Figure 13.1.
Structure of thiamine (left) and thiaminepyrophosphate (TPP, right).
