PAH-Nucleoside Adduct Synthesis by I2 Oxidation
Chem. Res. Toxicol., Vol. 11, No. 10, 1998 1203
7.93 (m, 1H, 3-H), 7.99 (s, 1H, 8-H[Gua]), 8.23 (d, J ) 9.0 Hz,
1H, 6-H), 8.44 (m, 1H, 11-H), 8.52 (m, 2H, 1-H, 8-H), 10.15 (bs,
1H, 1-NH[Gua]). UV: λmax 264, 286, 296, 349, 364, 380 nm.
FAB MS [M + H]+: calcd for C30H27N5O4 m/z 522.2141, found
m/z 522.2131.
Resu lts a n d Discu ssion
Op tim iza tion of Rea ction Con d ition s. Reactions
were conducted to determine whether one-electron oxida-
tion by I2 would produce adequate yields of PAH-
nucleoside adducts. To optimize the yield of PAH-
nucleoside adducts, 59 µmol (15 mg) of BP was added to
varying equivalents (equiv) of dG, I2, and AgClO4 in 6
mL of DMF at room temperature for 18 h. The best ratio
was found to be 1:5:3:1 PAH:dG:I2:AgClO4. Smaller
amounts of I2 resulted in low yields (<10% adduct),
whereas amounts greater than 3 equiv did not improve
the yield. Increasing the ratio of AgClO4 decreased the
yield of 7-(benzo[a]pyren-6-yl)guanine (BP-6-N7Gua) due
to the formation of 6-I-BP. The yield of the BP-6-N7Gua
adduct was most dependent on the amount of AgClO4
used in the reaction mixture. More than 1 equiv of
AgClO4 produced low amounts of adduct and high
amounts of the byproduct 6-I-BP. At 6 equiv of AgClO4,
92% of the BP was converted to 6-I-BP. Less than 1
equiv produced low yields of both the adduct and byprod-
uct. Therefore, the ratio of reactants stated above was
used for oxidation of BP, DB[a,l]P, and DMBA in the
presence of dG, Gua, dA, or Ade in the solvent DMF or
Me2SO, with or without AgClO4. Gua was used only with
Me2SO due to its extremely low solubility in DMF.
F igu r e 1. HPLC separation of adducts formed by I2 oxidation
of BP in the presence of Ade and AgClO4. (A) The HPLC column
was eluted with 40% CH3CN in H2O for 15 min, followed by a
15 min linear gradient to 60% CH3CN in H2O, at which the
mixture was held for 10 min, followed by a 10 min linear
gradient to 100% CH3CN. (B) The HPLC column was eluted
with 65% C2H5OH/CH3CN (3:1) in H2O for 15 min, followed by
a 25 min linear gradient to 100% C2H5OH/CH3CN (3:1).
12-MBA-7-CH2-N1Ad e. 1H NMR (ppm): δ 3.39 (s, 3H, 12-
CH3), 6.52 (s, 2H, 7-CH2), 7.54 (s, 1H, 2-H[Ade]), 7.65 (m, 3H,
3-H, 4-H, 9-H), 7.72 (m, 1H, 2-H), 7.75 (d, J ) 9.5 Hz, 1H, 5-H),
7.81 (bs, 1H, 6-NH[Ade]), 7.94 (m, 2H, 10-H, 6-NH[Ade]), 7.95
(s, 1H, 8-H[Ade]), 8.25 (d, J ) 9.5 Hz, 1H, 6-H), 8.48 (m, 2H,
1-H, 11-H), 8.54 (m, 1H, 8-H). UV: λmax 266, 288, 298, 352,
367, 384 nm. FAB MS [M + H]+: calcd for C25H19N5 m/z
390.1719, found m/z 390.1729.
7-MBA-12-CH2-N3Ad e. 1H NMR (ppm): δ 3.14 (s, 3H,
7-CH3), 6.22 (s, 2H, 12-CH2), 7.32 (bs, 2H, 6-NH2[Ade]), 7.42
(m, 1H, 2-H), 7.56 (s, 1H, 2-H[Ade]), 7.59 (m, 1H, 10-H), 7.66
(m, 2H, 3-H, 9-H), 7.78 (d, J ) 10.0 Hz, 1H, 5-H), 7.97 (m, 3H,
1-H, 4-H, 11-H), 8.23 (d, J ) 9.0 Hz, 1H, 6-H), 8.29 (s, 1H,
8-H[Ade]), 8.51 (d, J ) 9.0 Hz, 1H, 8-H). UV: λmax 266, 286,
297, 347, 364, 379 nm. FAB MS [M + H]+: calcd for C25H19N5
m/z 390.1719, found m/z 390.1708.
The better yield of the reactions in the presence of the
proper amount of AgClO4 is presumably due to stabiliza-
tion of the radical cation as a perchlorate (17, 18),
produced after one-electron oxidation of the PAH by I2.
It was observed, however, that with a large amount of
AgClO4, BP is almost totally converted to 6-I-BP, sug-
gesting that formation of AgI from I2 efficiently generates
the electrophilic I+ that reacts to form 6-I-BP.
Syn th esis of Un su bstitu ted P AH-Nu cleosid e Ad -
d u cts. Formation of unsubstituted PAH adducts can be
rationalized with initial removal of one electron by I2
(Scheme 1). The intermediate radical cation, with charge
localized at C-6 in BP (Scheme 1) or C-10 in DB[a,l]P,
regiospecifically reacts with nucleophilic groups of nu-
cleosides or nucleobases to form an intermediate radical
species, with loss of the proton from the N-9 of Ade (Gua)
or cleavage of the glycosidic bond with dA (dG) to lose
deoxyribose. The easy removal of a second electron from
the arene radical by either I2 or another BP radical cation
produces an arenium ion, which loses a proton to
complete the substitution reaction.
12-MBA-7-CH2-N3Ad e. 1H NMR (ppm): δ 3.39 (s, 3H, 12-
CH3), 6.28 (s, 2H, 7-CH2), 7.23 (bs, 1H, 6-NH[Ade]), 7.48 (s, 1H,
2-H[Ade]), 7.65 (m, 2H, 2-H, 3-H), 7.70 (m, 2H, 9-H, 10-H), 7.76
(d, J ) 9.0 Hz, 1H, 5-H), 7.94 (m, 1H, 4-H), 8.32 (s, 1H,
8-H[Ade]), 8.33 (d, J ) 8.5 Hz, 1H, 6-H), 8.46 (d, J ) 8.5 Hz,
1H, 11-H), 8.53 (m, 1H, 1-H), 8.57 (d, J ) 8.0 Hz, 1H, 8-H). UV:
λ
max 266, 285, 295, 348, 363, 379 nm. FAB MS [M + H]+: calcd
for C25H19N5 m/z 390.1719, found m/z 390.1708.
7-MBA-12-CH2-N2d G. 1H NMR (ppm): δ 2.22 (m, 1H, 2′-
H), 2.70 (m, 1H, 2′-H), 3.10 (s, 3H, 7-CH3), 3.49 (m, 1H, 5′-H),
3.55 (m, 1H, 5′-H), 3.78 (m, 1H, 4′-H), 4.34 (m, 1H, 3′-H), 4.82
(m, 1H, 5′-OH), 5.20 (d, J ) 3.5 Hz, 1H, 3′-OH), 5.30 (m, 2H,
12-CH2), 6.19 (t, J ) 7.0 Hz, 1H, 1′-H), 7.48 (bs, 1H, 2-NH[Gua]),
7.58 (m, 1H, 9-H), 7.66 (m, 1H, 4-H), 7.73 (m, 3-H, 2-H, 5-H,
10-H), 7.99 (s, 1H, 8-H[Gua]), 8.16 (d, J ) 10.0 Hz, 1H, 11-H),
8.34 (d, J ) 9.0 Hz, 1H, 6-H), 8.48 (dd, J 1,2 ) 9.0 Hz, J 8,9 ) 10.0
Hz, 2H, 1-H, 8-H), 10.27 (bs, 1H, 1-NH[Gua]). UV: λmax 264,
287, 297, 349, 364, 380 nm. FAB MS [M + H]+: calcd for
The unsubstituted PAH, BP and DB[a,l]P, reacted
similarly under identical conditions, as seen in Tables 2
and 3. All the adducts formed from dG and dA lose the
deoxyribose moiety by destabilization of the glycosidic
bond. Generally, the highest yields of adduct were
obtained from the reactions conducted in DMF in the
presence of AgClO4. Identical reaction mixtures in
Me2SO generally produced a lower yield compared to the
reactions in DMF. Gua, however, was reacted only in
Me2SO because of its poor solubility in DMF.
C
30H27N5O4 m/z 522.2141, found m/z 522.2141.
12-MBA-7-CH2-N2d G. 1H NMR (ppm): δ 2.33 (m, 1H, 2′-
H), 2.69 (m, 1H, 2′-H), 3.33 (s, 3H, 12-CH3), 3.58 (m, 1H, 5′-H),
3.63 (m, 1H, 5′-H), 3.89 (s, 1H, 4′-H), 4.44 (s, 1H, 3′-H), 4.97
(bs, 1H, 5′-OH), 5.40 (s, 1H, 3′-OH), 5.43 (s, 2H, 7-CH2), 6.38 (t,
J ) 6.75 Hz, 1H, 1′-H), 6.92 (bs, 1H, 2-NH[Gua]), 7.64 (m, 2H,
2-H, 4-H), 7.73 (m, 2H, 9-H, 10-H), 7.78 (d, J ) 9.5 Hz, 1H, 5-H),
Reaction of BP or DB[a,l]P with dG, Gua, dA, or Ade
produced an array of adducts, which can be used as