P. Yu. Lagutin, O. I. Shadyro / Bioorg. Med. Chem. Lett. 15 (2005) 3797–3800
3799
Shimadzu instrument equipped with an EC 250/4 Nucle-
osil Carbohydrate column. Analysis conditions include:
flow rate: 1 ml/min; mobile phase: acetonitrile/water (80/
20 v/v); loop 20 ll; refractometric detector RID (Aux.-
rang.1; Response 5). All the data presented were ob-
tained by averaging the results of at least three series
of experiments. The yields of product formation were
determined from relationships between accumulation
of the respective products and the dose absorbed.
vitamins B1 and B6, a drastic drop in 2,3-butanediol
yields can be noted (see Table 1). Because acetaldehyde
yields decrease to aÅlesser extent, one can presume that
interactions of CH3 CHOH radicals with these vitamins
are not restricted to just the reaction (10). Since the
structures of vitamins B1 and B6 contain –C@N– double
bonds, these substances can, similar to quinonimines
Å
and riboflavine (B2), partially oxidize CH3 CHOH radi-
cals according to reaction (9) to form acetaldehyde.
Å
The data on final product yields obtained after radioly-
sis of the systems under study are shown in Table 1.
Unlike CH3 CHOH species, radicals formed from ethyl-
ene glycol15 and carbohydrates10,11 are able to undergo
fragmentation reactions, which, as noted previously,
cause damage to many biologically important substances.
In the case of fragmentation of ethylene glycol radicals
according to reactions (5,6), acetaldehyde is formed. On
changing from 1 to 3 M solutions, the process appears
to switch to a chain mechanism, because acetaldehyde
yields are higher than that of the initiator (GOH ꢁ 2.8)
in this case. Group B vitamins block the process (5),
and, depending on the vitamin structure, this is realized
according to different mechanisms. Thus, inhibition of
acetaldehyde formation on radiolysis of ethylene glycol
in the presence of vitamin B2 and PPh is accompanied
by an increase in yields of glycolic aldehyde, which points
to the ability of these substances to oxidize HOÅCH-
CH2OH radicals according to a reaction of type (9). Vita-
mins B1 and B6 are more liable to block fragmentation
reactions of ethylene glycol radicals by both reduction
according to reaction (10) and oxidation according to
reaction (9), leadingto a decrease in yields of acetaldehyde
and a slight increase in yields of glycolic aldehyde.
While analyzing the data given in the table, one can
ascertain that B group vitamins are reactive toward var-
ious a-hydroxyl-containing radicals, and that they are
able to modify transformation pathways of the latter
to a substantial extent. Thus, on radiolysis of aqueous
ethanol solutions, all the B group vitamins studied de-
crease 2,3-butanediol yields significantly, while sup-
Å
pressing recombination reactions of CH3 CHOH
species. At the same time, vitamin B2 and PPh substan-
tially increased the yield of acetaldehyde, an oxidation
product of a-hydroxyethyl radicals. Quinones,17 qui-
nonimines,18, and aldehydes19 are known to oxidize
a-hydroxyethyl radicals effectively. Since vitamin B2
and PPh contain similar structural moieties, they also
react as given below:
Å
Å
CH3 CHOH þ B ! CH3CHO þ BH
B = B2, PPh
ð9Þ
The realization of reaction (9) accounts for the observed
effects of suppression of the 2,3-butanediol yields and in-
crease in acetaldehyde yields on radiolysis of aqueous
ethanol solutions in the presence of vitamin B2 and PPh.
Fragmentation reaction of carbohydrate radicals (8),
leading to cleavage of the O-glycoside bond, is effectively
blocked by vitamin B1 and PPh, as evidenced by the
data given in the table. This fact appears to be impor-
tant, because, as shown in our recent study,5 a reaction
similar to (8) taking place upon action of free-radical
reaction initiators on cerebrosides leads to their destruc-
tion with the formation of ceramides involved in the
regulation of apoptotic processes.
Molecules of vitamins B1 and B6 contain an amino- and
a hydroxyl group, respectively, and hence these sub-
stances are able to reduce organic radicals according
to reaction (10), similar to phenols20 and aromatic
amines18,21
:
Å
Å
CH3 CHOH þ BXH ! CH3CH2OH þ B X
X = –NH– (B1), –O– (B6)
ð10Þ
The data obtained in this study indicate that group B vita-
mins possess some new properties associated with their
capability of regulating free-radical reactions involving
carbon-centered a-hydroxyl-containing radicals. Reac-
tions of this type can lead to destruction of biologically
Reaction (10) should lead to a decrease in yields of acet-
aldehyde and 2,3-butanediol. Indeed, in the presence of
Table 1. Product yields (G) obtained from radiolysis of aqueous ethanol, ethylene glycol, a-methylglycoside, and maltose solutions in the presence of
group B vitamins
Initial system
Products
G Æ 107 (mol/J)
Ar
B1
B2
B6
PPh
Ethanol, 1 M
Acetaldehyde
2,3-Butanediol
0.33 0.10
1.68 0.14
0.57 0.07
0.05 0.01
3.56 0.20
0.07 0.01
0.58 0.05
0.05 0.01
3.98 0.18
0.04 0.01
Ethylene glycol, 1 M
Ethylene glycol, 3 M
Acetaldehyde
Glycolic aldehyde
3.21 0.14
1.18 0.10
0.18 0.03
1.09 0.15
0.36 0.05
4.34 0.25
0.32 0.09
1.76 0.15
0.11 0.03
5.13 0.37
Acetaldehyde
Glycolic aldehyde
12.4 0.97
0.88 0.13
0.44 0.03
1.37 0.15
0.54 0.10
4.05 0.78
1.61 0.20
1.71 0.25
0.30 0.05
4.50 0.36
a-Methylglycoside, 0.1 M
Maltose, 0.1 M
Methanol
Glucose
1.71 0.11
1.20 0.10
0.31 0.03
0.10 0.04
1.18 0.06
—
1.46 0.04
1.07 0.11
0.43 0.03
—