Independent Generation and Reactivity of 2′-Deoxy-5-methyleneuridin-5-yl, a Significant Reactive Intermediate Produced from Thymidine as a Result of Oxidative Stress

Article abstract of DOI:10.1021/jo000271s

2′-Deoxy-5-methyleneuridin-5-yl (1) is produced in a variety of DNA damage processes and is believed to result in the formation of lesions that are mutagenic and refractory to enzymatic repair. 2′-Deoxy-5-methyleneuridin-5-yl (1) was independently generated under anaerobic conditions via Norrish Type I photocleavage during Pyrex filtered photolysis of the benzyl ketone 7. The radical (1) exhibits behavior consistent with that of a resonance-stabilized radical. The KIE for hydrogen atom transfer from t-BuSH was found to be 7.3 ± 1.7. Competition studies between radical recombination and hydrogen atom donors (2,5-dimethyltetrahydrofuran, k_Trap = 46.1 ± 15.4 M^-1 s^-1; propan-2-ol, k_Trap = 13.6 ± 3.5 M^-1 s^-1) chosen to mimic the carbohydrate components of 2′-deoxyribonucleotides suggest that 2′-deoxy-5-methyleneuridin-5-yl (1) may be able to transfer damage from the nucleobase to the deoxyribose of an adjacent nucleotide in DNA under hypoxic conditions.

Full text of DOI:10.1021/jo000271s

4648
J . Org. Chem. 2000, 65, 4648-4654
In d ep en d en t Gen er a tion a n d Rea ctivity of
2′-Deoxy-5-m eth ylen eu r id in -5-yl, a Sign ifica n t Rea ctive
In ter m ed ia te P r od u ced fr om Th ym id in e a s a Resu lt of Oxid a tive
Str ess
Aaron S. Anderson, J ae-Taeg Hwang, and Marc M. Greenberg*
Department of Chemistry, Colorado State University Fort Collins, Colorado 80523
mgreenbe@lamar.colostate.edu
Received February 26, 2000
2′-Deoxy-5-methyleneuridin-5-yl (1) is produced in a variety of DNA damage processes and is
believed to result in the formation of lesions that are mutagenic and refractory to enzymatic repair.
2′-Deoxy-5-methyleneuridin-5-yl (1) was independently generated under anaerobic conditions via
Norrish Type I photocleavage during Pyrex filtered photolysis of the benzyl ketone 7. The radical
(1) exhibits behavior consistent with that of a resonance-stabilized radical. The KIE for hydrogen
atom transfer from t-BuSH was found to be 7.3 ( 1.7. Competition studies between radical
recombination and hydrogen atom donors (2,5-dimethyltetrahydrofuran, kTrap ) 46.1 ( 15.4 M-1
s-1; propan-2-ol, kTrap ) 13.6 ( 3.5 M-1 s-1) chosen to mimic the carbohydrate components of 2′-
deoxyribonucleotides suggest that 2′-deoxy-5-methyleneuridin-5-yl (1) may be able to transfer
damage from the nucleobase to the deoxyribose of an adjacent nucleotide in DNA under hypoxic
conditions.
Sch em e 1
Ionizing radiation (γ-radiolysis, UV-irradiation) is a
general and effective means for inducing nucleic acid
damage.1 The carbohydrate centered radicals produced
by many of the well-studied antitumor antibiotics (e.g.,
bleomycin) are included among the abundant group of
reactive intermediates resulting from the interaction of
nucleic acids with ionizing radiation.2,3 Nucleobase radi-
cals and radical ions constitute a significant portion of
species produced via the interaction of ionizing radiation
with nucleic acids and represent a group of reactive
intermediates that are unique to this method of inducing
nucleic acid damage and related radiomimetic systems.2,4-6
Pyrimidine radicals resulting from direct and/or formal
radical addition to the 5,6-double bond have been studied
under ionizing radiation conditions and by using chemical
precursors designed to generate specific radicals.1,2,5 The
latter method has facilitated examination of the reactivity
of these nucleobase radicals and resulted in the charac-
terization of an unusual mechanism for the formation of
tandem lesions in DNA.7 The nucleobase radical 1
resulting from formal hydrogen atom abstraction from
the methyl group of thymidine has garnered increasing
attention. In addition to being formed by direct hydrogen
atom abstraction, 2′-deoxy-5-methyleneuridin-5-yl (1) is
produced from the pyrimidine cation radical via depro-
tonation (Scheme 1).8-10 It has also been suggested to
result from initial intramolecular hydrogen atom ab-
straction, following photoionization.11 We describe herein
initial experiments in our group on the independent
generation and study of the reactivity of 2′-deoxy-5-
methyleneuridin-5-yl (1).12
2′-Deoxy-5-methyleneuridin-5-yl (1) has been impli-
cated in a number of DNA damage processes. Under
(7) (a) Greenberg, M. M.; Barvian, M. R.; Cook, G. P.; Goodman, B.
K.; Matray, T. J .; Tronche, C.; Venkatesan, H. J . Am. Chem. Soc. 1997,
119, 1828. (b) Tallman, K. A.; Greenberg, M. M. Submitted for
publication.
(1) von Sonntag, C. The Chemical Basis of Radiation Biology; Taylor
& Francis: London, 1987.
(2) Greenberg, M. M. In Comprehensive Natural Products Chemistry,
Vol. VII, DNA and Aspects of Molecular Biology; Kool, E. T., Ed.;
Pergammon Press: Oxford, 1999; p 371.
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(b) Pratviel, G.; Bernadou, J .; Meunier, B. Angew. Chem., Int. Ed. Engl.
1995, 34, 746.
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(5) Greenberg, M. M. Chem. Res. Toxicol. 1998, 11, 1235.
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Biol. Chem. 1989, 264, 20509. (b) Dizdaroglu, M.; Aruoma, O. I.;
Halliwell, B. Biochemistry 1990, 29, 8447.
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Chem. Soc., Perkin Trans. 2 1988, 1303. (c) Lange, L.; Weiland, B.;
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10.1021/jo000271s CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/01/2000

Generation of 2′-Deoxy-5-methyleneuridin-5-yl
J . Org. Chem., Vol. 65, No. 15, 2000 4649
Sch em e 2
aerobic conditions, formation of 1 is believed to give rise
to thymidine derivatives that are oxidatively modified at
the C5-methyl group.13 One of these oxidatively modified
thymidines, the C5-formyl nucleotide 2 has been shown
to be a premutagenic lesion and inhibits restriction
enzyme activity.14 2′-Deoxy-5-methyleneuridin-5-yl (1) is
believed to result in the formation of tandem lesions 3
and 4 under anaerobic and aerobic conditions, respec-
tively.15,16 Tandem lesion 3 is the major lesion identified
Resu lts a n d Discu ssion
Design a n d Syn th esis of a P h otoch em ica l P r e-
cu r sor for 2′-Deoxy-5-m eth ylen eu r id in -5-yl (1). The
Norrish Type I photochemical reaction has been success-
fully employed in the generation of several radicals that
are involved in DNA damage processes.2,7a,18 We antici-
pated that either the tert-butyl (6) or benzyl (7) ketones
would be reasonable precursors for 1. Competition be-
tween which carbon-carbon bond would cleave initially
was not a concern (Scheme 2). We expected that the
resonance stabilization of 1 would induce a sufficiently
high driving force such that bimolecular reactions (e.g.,
thiol trapping) would not compete with decarbonylation
from 8.19 The bis-silyl tert-butyl ketone 9 was prepared
by a direct but low yielding route via alkylation of the
carbanion.20 The major product was the result of N-
alkylation. Synthesis of the benzyl ketone was not
amenable to this approach. Instead, 7 was synthesized
by condensing the lithiated dithiane of phenylacetaldeyde
with the allylic bromide 10, followed by cleavage of the
dithiane protecting group (Scheme 3).21 The deprotected
ketones 6 and 7 were obtained following fluoride medi-
ated desilylation.
in a tetranucleotide following γ-radiolysis under anaero-
bic conditions. Photoproduct 5, a tandem lesion putatively
involving an adjacent thymidine and 1, is also formed in
significant amounts in bacterial spores and under other
conditions of low humidity.17 Thermodynamic consider-
ations and experimental evidence suggest that 1 is
inefficient at effecting hydrogen atom abstraction from
carbon-hydrogen bonds.8b However, this pathway is
difficult to investigate in experiments involving genera-
tion of 1 from thymidine because the product of the
radical reaction is the substrate. Whether 1 abstracts a
hydrogen atom from the carbohydrate component of a
deoxyribonucleotide in DNA is important, as such a
process is required for the formation of direct strand
breaks from this nucleobase radical under anaerobic
conditions. We anticipated that this issue and others
concerning the reactivity of 1 could be addressed by
independently generating the nucleobase radical from a
chemically synthesized precursor.
P h otoch em ica l Ch a r a cter iza tion of 6 a n d 7 a n d
In d ep en d en t Syn th esis of P oten tia l P h otop r od u cts.
Ketones 6 and 7 proved to be stable to extended irradia-
tion at λmax ) 350 nm. Similarly, the tert-butyl ketone
was also relatively inert to irradiation at λmax ) 300 nm.
However, evidence for the formation of 1 from the benzyl
ketone (7, 5 mM) in the presence of 2-mercaptoethanol
(BME, 50 mM) was gleaned from the formation of
thymidine. The yield of thymidine was 40% (based upon
unrecovered starting material) and was found to decrease
slightly with increasing conversion of ketone. While
(12) While this manuscript was under review an independent report
concerning the independent generation and study of 1 appeared. Please
see: Romieu, A.; Bellon, S.; Gasparutto, D.; Cadet, J . Org. Lett. 2000,
2, 1085.
(13) Bjelland, S.; Eide, L.; Time, R. W.; Stote, R.; Eftedal, I.; Volden,
G.; Seeberg, E. Biochemistry 1995, 34, 14758.
(14) (a) Zhang, Q.-M.; Sugiyama, H.; Miyabe, I.; Matsuda, S.; Kino,
K.; Saito, I.; Yonei, S. Int. J . Radiat. Biol. 1999, 75, 59. (b) Zhang,
Q.-M.; Sugiyama, H.; Miyabe, I.; Matsuda, S.; Saito, I.; Yonei, S. Nucleic
Acids Res. 1997, 25, 3969.
(15) (a) Box, H. C.; Budzinski, E. E.; Dawidzik, J . D.; Wallace, J .
C.; Evans, M. S.; Gobey, J . S. Radiat. Res. 1996, 145, 641. (b)
Budzinski, E. E.; Dawidzik, J . D.; Rajecki, M. J .; Wallace, J . C.;
Schroder, E. A.; Box, H. C. Int. J . Radiat. Biol. 1997, 71, 327.
(16) Delatour, T.; Douki, T.; Gasparutto, D.; Brochier, M.-C.; Cadet,
J . Chem. Res. Toxicol. 1998, 11, 1005.
(18) (a) Hwang, J . T.; Greenberg, M. M. J . Am. Chem. Soc. 1999,
121, 1, 4311. (b) Goodman, B. K.; Greenberg, M. M. J . Org. Chem. 1996,
61, 2.
(19) (a) Lunazzi, L.; Ingold, K. U.; Scaiano, J . C. J . Phys. Chem.
1983, 87, 529. (b) Hany, R.; Fischer, H. J . Chem. Phys. 1993, 172, 131.
(20) Armstrong, R. W.; Gupta, S.; Whelihan, F. Tetrahedron Lett.
1989, 30, 2057.
(17) (a) Begley, T. P. In Comprehensive Natural Products Chemistry,
Vol. V, Enzymes, Enzyme Mechanisms, Proteins, and Aspects of NO
Chemistry; Poulter, C. D., Ed.; Pergammon Press: Oxford, 1999; p 371.
(b) Mehl, R. A.; Begley, T. P. Org. Lett. 1999, 1, 1065.
(21) Seebach, D.; Corey, E. J . J . Org. Chem. 1975, 40, 231.

4650 J . Org. Chem., Vol. 65, No. 15, 2000
Anderson et al.
Sch em e 3
to be the symmetrical dimer 18. Formation of this product
was eliminated upon addition of 50 mM BME. In addi-
tion, inclusion of BME in the photolysis samples also
resulted in the formation of small amounts of the
photoreduction product 13 (2-9% based upon the amount
of 7 consumed). In contrast, the acyl radical trapping
product 15 was not detected in the presence of BME
ranging from 10 to 200 mM. However, the detection of
small amounts of 15 (<10%) was compromised due to
equilibration of the aldehyde in protic solvents to yield a
mixture of the free carbonyl, hydrate, hemiacetal, and
acetal. The formation of thymidine and 13-15 did not
account for 100% of the ketone 7 consumed. Conse-
quently, the possibility that thymidine was unstable
under the photolysis conditions was explored.24 Extended
(12 h) irradiation of thymidine (5 mM) in the presence
of BME (50 mM) resulted in isolation of a diastereomeric
mixture of adduct 19. However, HPLC analysis revealed
Sch em e 4
that this adduct was not produced under the analytical
photolysis conditions. In principle, the benzyl ketone 7
can undergo an analogous photochemical reaction with
BME. While no evidence was obtained for such an adduct,
or any subsequent decomposition product(s), this photo-
chemical pathway cannot be discounted.25 Despite this
limitation, mass balances of >65% were consistently
obtained by reducing the number of equivalents of thiol
relative to 7 to 5, and curtailing irradiation times so as
to maintain photoconversion of 7 to <50%.
Hyd r ogen Atom Abstr a ction by 2′-d eoxy-5-m eth -
ylen eu r id in -5-yl (1). The proclivity with which 1 ab-
stracts hydrogen atoms from the deoxyribose ring in DNA
determines its ability to participate in direct strand break
formation. Insight into this possibility was sought by
examining the ability of 1 to abstract hydrogen atoms
from model compounds of the carbohydrate component
of nucleotides. 2,5-Dimethyltetrahydrofuran, propan-2-
ol, and ethanol were chosen to mimic the C1′, C4′, and
C5′ positions of the sugars, respectively. These molecules
were also chosen as model substrates, because they could
be employed in high concentration in order to mimic the
potential effective molarity of a deoxyribonucleotide
adjacent to 1 in DNA. Additionally, their volatility
thymidine was the product of the desired photochemical
formation of 1 in the presence of hydrogen atom donors,
the syntheses of several other potential products were
carried out in order to facilitate a more complete char-
acterization of the photochemical behavior of 7 (Scheme
4).
The product resulting from the photoreduction of the
ketone group (13) was prepared as a mixture of diaster-
eomers from 12. The recombination product 14 was
obtained following hydrogenation of 16, which was
prepared from bis-silylated 5-iodo-2′-deoxyuridine via a
Heck coupling.22 Finally, the bis-silyl precursor (17) of
the product resulting from trapping of the acyl radical
formed upon Type I cleavage (15) was prepared using
the method of Glick.23
Irradiation of 7 in the absence of BME gave rise to
recombination product 14 in 73% yield based upon the
amount of unrecovered ketone. In addition, small amounts
of a product which had a molecular weight equal to twice
that of 1 were isolated by HPLC and characterized by
mass spectrometry. This product is tentatively believed
(24) (a) Shetlar, M. D.; Hom, K. Photochem. Photobiol. 1987, 45,
703. (b) J ellinek, T.; J ohns, R. B. Photochem. Photobiol. 1970, 11, 349.
(25) In principle, the analogous BME addition product to 7 could
undergo subsequent Type I cleavage to yield 18. This adduct could
also undergo intramolecular hydrogen atom transfer to yield Norrish
Type II and Yang type products. For reviews of this subject, see: (a)
Wagner, P.; Park, B.-S. Org. Photochem. 1991, 11, 227. (b) Descotes,
G. L. In CRC Handbook of Organic Photochemistry and Photobiology;
Horspool, W. M., Song, P.-S., Eds.; CRC Press: Boca Raton, FL, 1995.
(22) (a) Selvidge, S. D., III; J ang, J .; Ray, P. S. Nucleosides
Nucleotides 1997, 16, 2019. (b) Bigge, C. F.; Kalaritis, P.; Deck, J . R.;
Mertes, M. P. J . Am. Chem. Soc. 1980, 102, 2033.
(23) Osborne, S. E.; Cain, R. J .; Glick, G. D. J . Am. Chem. Soc. 1997,
119, 1171.

Generation of 2′-Deoxy-5-methyleneuridin-5-yl
J . Org. Chem., Vol. 65, No. 15, 2000 4651
The ability of the recombination product (14) of 4 and
benzyl radical to compete with thiol trapping suggested
that this process may also be used as a clock reaction for
estimating the rate of hydrogen atom abstaction from
models of the carbohydrate component of deoxyribonu-
cleotides. This is fortunate, because employing the reac-
tion of 1 with t-BuSD as a clock reaction proved difficult
due to the formation of significant (attributable to the
large KIE) and variable amounts of [1H]thymidine,
presumably resulting from trace amounts of a hydrogen
atom source. Consequently, the rate constants for hy-
drogen atom abstraction from the above-mentioned model
compounds by 1 were estimated by measuring the ratio
of thymidine: recombination product 14 as a function of
trap concentration (eq 1). On the basis of mechanistic
studies of the Norrish Type I photochemical reaction, we
believe that 14 is formed via freely diffusing radicals.29
The rate constant for recombination (kRec) employed was
F igu r e 1. Kinetic isotope effect for the reaction of 1 with tert-
butylthiol.
2 × 109 M-1 s-1 30
. This value for kRec should be considered
to be a lower limit for this process. Any increase in kRec
would result in a proportional increase in the estimate
of kT (Scheme 4, eq 1). The steady-state concentration of
benzyl radical was estimated by assuming the that
velocity of the Type I process was constant at the low
conversions of ketone employed. Hence, the steady-state
concentration of benzyl radical was determined on the
basis of the concentration of ketone converted (measured
by HPLC for each sample) over the time of irradiation
(720 s). No thymidine was observed when 7 was photo-
lyzed in the presence of ethanol (maximum [EtOH] ) 11.4
M). However, varying amounts of thymidine were formed
when 7 was irradiated in the presence of propan-2-ol
(3.9-6.5 M) or 2,5-dimethyltetrahydrofuran (2.5-4.2 M).
In addition to the formation of thymidine and 14, small
amounts (<10%) of photoreduction product 13 were also
observed under these conditions, particularly when 7 was
irradiated in the presence of increasing amounts of 2,5-
dimethyltetrahydrofuran. The average rate constants
determined for trapping of 4 by 2,5-dimethyltetrahydro-
furan and propan-2-ol were found to be 46.1 ( 15.4 and
facilitates sample analysis. Attempts to approximate the
rate constants for reaction of 1 with these hydrogen atom
donors were made by using formation of recombination
product 14 and reaction with deuterated thiols as com-
peting processes, or “clock” reactions.
Estimates of rate constants for hydrogen atom abstrac-
tion from the model substrates could potentially be
determined by competition with thiols which trap alkyl
radicals at known rate constants. Since in the current
experiment deuterated thiols are required in order to
distinguish between reaction with the model substates
and the clock reaction thiol, it was necessary to measure
the KIE for the reaction between 1 and t-BuSH. The KIE
(7.3 ( 1.7) for the transfer from t-BuSH was determined
from the slope of a plot of [1H]thymidine:[2H]thymidine
over a range of t-BuSH:t-BuSD ratios in order to remove
any contribution of background processes to the forma-
tion of [1H]thymidine (Figure 1). The ratio of t-BuSH:t-
1
BuSD was determined directly by H NMR in order to
take into account the equilibrium isotope effect of the
thiol fractionation in a mixture of H2O and D2O.26 The
ratio of [1H]thymidine:[2H]thymidine was determined by
analysis of the respective M - 15 ions of bis-trimethyl-
silylthymine obtained following formic acid cleavage of
crude photolyzates and accounting for the natural abun-
dance of the heavier (M + 1) isotopomer. As expected,
control experiments showed that no protons were ex-
changed from the C6 position of thymine under these
conditions. The magnitude of the KIE is within range of
analogous measurements reported for the reaction of
other resonance-stabilized alkyl radicals with thiols.27
The sizable KIE is also reflected by the observation that
a small but increasing amount of recombination product
14 was observed with increasing D2O content of the
solvent. Furthermore, in 100% D2O small amounts of 18
were also believed to be formed.28
13.6 ( 3.5 M-1 s-1
.
Su m m a r y. Pyrex filtered photolysis of benzyl ketone
7 provides an independent source of 2′-deoxy-5-methyl-
eneuridin-5-yl (1). Generation of 1 under anaerobic
conditions in the presence of hydrogen atom donors
produces thymidine. 2′-Deoxy-5-methyleneuridin-5-yl (1)
is also capable of abstracting hydrogen atoms from
molecules employed as mimics of the deoxyribose com-
ponent of nucleotides. The estimated bimolecular rate
constant derived from competition experiments involving
1 and 2,5-dimethyltetrahydrofuran is sufficiently high
that hydrogen atom abstraction from deoxyribonucleo-
tides in DNA may be able to compete to some extent with
(28) Small amounts of the dimer were isolated by HPLC and
analyzed by LRMS FAB (m/z obsd 482.1, calcd 482.5). GC/MS analysis
showed that the dimer did not decompose to thymine upon formic acid
treatment. Hence, formation of this product does not affect the analysis
of the reactions of 1 with hydrogen atom donors.
(29) Turro, N. J .; Chow, M. F.; Chung, C. J .; Tanimoto, Y.; Weed,
G. C. J . Am. Chem. Soc. 1981, 103, 4574.
(30) (a) Fischer, H.; Paul, H. Acc. Chem. Res. 1987, 20, 200. (b)
Claridge, R. F. C.; Fischer, H. J . Phys. Chem. 1983, 87, 1960. (c)
Arends, I. W. C. E.; Mulder, P.; Clark, K. B.; Wayner, D. D. M. J . Phys.
Chem. 1995, 99, 8182.
(26) (a) Szawelski, R. J .; Wharton, C. W.; White, S. Biochem. Soc.
Trans. 1982, 10, 232. (b) Hibbert, F.; Thomas, G. A. I. J . Chem. Soc.,
Perkin Trans. 2 1986, 1761.
(27) (a) Pryor, W. A.; Kniepp, K. G. J . Am. Chem. Soc. 1971, 93,
5584. (b) Work by Franz et al. suggests that the KIE for hydrogen
atom abstraction from thiophenol by benzyl radical may be significantly
smaller than those reported by Pryor and Kniepp. See: Franz, J . A.;
Suleman, N. K.; Alnajjar, M. S. J . Org. Chem. 1986, 51, 19.

4652 J . Org. Chem., Vol. 65, No. 15, 2000
Anderson et al.
MeOH:CH2Cl2 afforded thymidine and adduct 19 (6.6 mg, 19%
yield) as a mixture of diastereomers. 1H NMR (CD3OD) δ: 6.30
(dd, J ) 7.8, 6.3 Hz, 1H), 6.20 (dd, J ) 8.4, 6 Hz, 0.4H), 4.28
(m, 1.4H), 3.74-3.83 (m, 2.2H), 3.60-3.72 (m, 5.6H), 3.50 (m,
1.4H), 3.04 (ddd, J ) 18, 12, 3 Hz, 0.4H), 2.88-2.69 (m, 3.4H),
2.32-2.15 (m, 2H), 2.01 (ddd, J ) 10.2, 3.6, 3 Hz, 0.4H), 1.88
(d, J ) 1.2 Hz, 1.2 H), 1.52 (d, J ) 3.3 Hz, 3H). LRMS (FAB):
calcd (M+ + H) 321.4, found 321.1.
Kin etic Isotop e Effects. Pyrex tubes were prepared so as
to contain the following: 7 (2 mM), tert-butylthiol (25 mM),
and the appropriate solvent. The tubes contained various
volume ratios of H2O:D2O dissolved in CH3CN. The samples
were degassed, photolyzed (300 nm), and analyzed by HPLC
and GC/MS as above.
reduction by thiols (in vivo concentration ≈5 mM,
kRSH ≈ 106 M-1 s-1), provided the effective molarity of
the adjacent deoxyribonucleotides is sufficiently high
(>10 M). It should also be noted that the current
experiments do not address the competition between
hydrogen atom abstraction and addition to the double
bond of an adjacent nucleobase. Moreover, given the
nature of the above model experiments, and the number
of approximations made during the estimation of the
biomolecular trapping rate constants, this issue should
be addressed by directly studying the reactivity of 2′-
deoxy-5-methyleneuridin-5-yl (1) within DNA.
Com p etition betw een Hyd r ogen Atom Don or s a n d
Ben zyl Ra d ica l for Tr a p p in g of 1. Ketone 5 (2 mM),
hydrogen atom donor (2,5-DMTHF, i-PrOD, or EtOD; 30-60
vol %), and 3:1 CH3CN:D2O were added to Pyrex tubes. The
samples were degassed, photolyzed, and analyzed by HPLC
and GC/MS as above.
Exp er im en ta l Section
All reactions were carried out in oven-dried glassware under
an atmosphere of argon or nitrogen unless otherwise noted.
THF was freshly distilled from sodium benzophenone ketyl.
Chloroform, methanol, ethanol, propan-2-ol, 2,5-dimethyltet-
rahydrofuran, tetramethylethylenediamine (TMEDA), and
carbon tetrachloride were distilled from CaH2. Phenylacetal-
dehyde, 1,3-propanedithiol, boron trifluoride-diethyl etherate,
2-mercaptoethanol, and tert-butylthiol were distilled from
themselves. Acetonitrile was purified by filtration through
anhydrous CuSO4, followed by distillation from CaH2. N-
Bromosuccinimide was either recrystallized from water or
sublimed. Bis-trimethylsilyl trifluoroacetamide (BSTFA) was
used as received (Sigma). HPLC analysis was carried out using
a Waters gradient, multiwavelength detector, system equipped
with either Baseline or MacIntegrator software and a Rainin
autosampler. Separations were carried out using a Rainin
Microsorb-MV 100 Å C-18 reverse phase column using the
following gradient: solvent A, H2O:MeOH (95:5); solvent B.
MeOH; t ) 0-10 min, 100% A; t ) 10-35 min, 0-100% B
linearly; t ) 35-40 min, 0-100% A linearly. GC/MS was
performed using a Hewlett-Packard 5890 GC equipped with
a HP 5970 mass selective detector. The column used was a 50
m DB-1. Oven conditions were the following: initial temper-
ature 150 °C, rate 10 °C/min, final temperature 200 °C. Data
were collected using selected ion monitoring (m/z 255.1, 256.1).
Gen er a l P h otolysis a n d An a lysis P r oced u r es. The
following procedure was used for all anaerobic photolyses.
Reactant, trap, and solvent were added to Pyrex tubes. These
solutions were vortexed and then centrifuged in an IEC clinical
centrifuge. The tubes were degassed (freeze, pump 3 min,
thaw; 3 cycles), sealed in vacuo, and irradiated at the ap-
propriate wavelength (λmax ) 300, 350 nm) in a Rayonet
photoreactor (12 lamps). After irradiation, the tubes were
vortexed and centrifuged prior to cracking. The appropriate
amount of internal standard (2′-deoxyuridine) was added, and
the solutions were transferred to Kontes glass conical vials
and evaporated to dryness in a Savant speed-vac. The contents
of the conical vials were redissolved in an appropriate solvent
(methanol or 1:1 CH3OH/NH4+HCOO-, 25 mM, pH 6.2) and
transferred to HPLC vials for HPLC analysis.
For GC/MS analysis, the samples were prepared as above
for HPLC, until just after the evaporation of the reaction
mixture. The dry reaction mixture was dissolved in an ap-
propriate solvent and a portion (usually 50 µL from 100 µL of
solution) was removed for HPLC analysis. To the remaining
solution was added formic acid (∼450 µL to 50 µL of solution),
and the solution was heated to 100 °C for 1 h. The solutions
were lyophilized and then dried azeotropically from EtOH (3
× 50 µL). BSTFA (25-50 µL) was added to the residue,
followed by heating at 100 °C for 2 h. GC/MS analysis was
performed by injecting approximately 1 µL of each silylated
solution.
P r ep a r a tive-Sca le Th iol P h otoa d d ition to Th ym id in e.
Thymidine (26.1 mg, 5 mM) was photolyzed at 300 nm under
degassed conditions (freeze, pump 4 min, thaw; 4 cycles) for
12 h in the presence of either 2-mercaptoethanol (50 mM) in
3:1 CH3CN:H2O (20 mL). The solvent and thiol were removed
in vacuo. Flash chromatography on silica gel eluting with 10%
1,3-Dith ia n e of P h en yla ceta ld eh yd e. Chloroform (83
mL), phenylacetaldehyde (2.00 g, 16.6 mmol), and 1,3-pro-
panedithiol (1.80 g, 16.6 mmol) were added to a 250 mL round-
bottomed flask. The reaction was cooled to -20 °C, and BF3‚
OEt2 (210 µL, 236 mg, 1.66 mmol) was added. The solution
was heated at reflux for 45 min and then cooled to room
temperature. Distilled water was added to the reaction mix-
ture. The solution was transferred to a separatory funnel, and
the organic layer was washed with water, 10% aqueous KOH,
and water. The organic layer was dried over MgSO4, filtered,
and concentrated in vacuo. Flash column chromatography on
silica gel eluting with 25% EtOAc:hexanes afforded the dithio-
acetal as a viscous oil that became a white solid upon freezing
1
(3.11 g, 91%). H NMR (CDCl3) δ ) 7.27 (m, 5H), 4.24 (t, J )
7.2 Hz, 1H), 3.11 (d, J ) 7.2 Hz, 2H), 2.85 (m, 4H), 2.19 (m,
1H), 1.95 (m, 1H).
3′,5′-Bis-O-(ter t-bu tyld im eth ylsilyl)-5-(br om om eth yl)-
2′-d eoxyu r id in e (10). 3′,5′-Bis-O-(tert-butyldimethylsilyl)-
thymidine (5.80 g, 12.32 mmol), N-bromosuccinimide (4.60 g,
25.9 mmol), and benzoyl peroxide (89 mg, 0.37 mmol) were
placed in a 250-mL round-bottom flask. Carbon tetrachloride
(123 mL) was added via syringe. The reaction was heated at
reflux for 1 h, during which time the solution changed from
colorless to orange. The reaction was allowed to cool and was
vacuum filtered through a fritted funnel to remove excess NBS
and succinimide. The solvent was removed from the filtrate
in vacuo by rotary evaporation to yield a crude yellow solid.
Flash column chromatography on silica gel eluting with 4:1
hexanes:EtOAc afforded the bromide (10) as an off-white solid
(3.08 g, 46%): mp 59-62 °C. 1H NMR (CDCl3) δ: 8.10 (s, 1H),
7.91 (s, 1H), 6.31 (dd, J ) 6, 1.8 Hz, 1H), 4.41 (m, 1H), 4.31
(d, J ) 10.8 Hz, 1H), 4.23 (d, J ) 10.8 Hz, 1H), 3.99 (t, J ) 2.4
Hz, 1H), 3.91 (dd, J ) 2.4, 11.1 Hz, 1H) 3.79 (dd, J ) 2.4, 11.1
Hz, 1H), 2.33 (m, 1H), 2.01 (m, 1H), 0.98 (s, 9H), 0.92 (s, 9H),
0.17 (s, 6H), 0.05 (s, 6H). 13C NMR (CDCl3) δ: 161.7, 149.8,
139.2, 111.7, 88.1, 85.5, 72.2, 63.0, 41.8, 25.9, 25.7, 25.1, 18.4,
17.9, -4.7, -4.9, -5.4. IR (film): 2930, 1711, 1463, 1254, 1098,
835 cm-1. HRMS (FAB): C22H41BrN2O5Si2 calcd (M+ + H)
549.1816, found 549.1802.
3′,5′-Bis-O-(ter t-bu tyldim eth ylsilyl)-5-(3-ph en yl-2,2-(1,3-
d ith io))p r op yl-2′-d eoxyu r id in e (11). The dithioacetal pre-
pared from phenylacetaldehyde (702 mg, 3.34 mmol) and THF
(13.3 mL) were placed in a 100-mL round-bottomed flask and
cooled to -40 °C. n-Butyllithium (1.9 M solution in cyclohex-
ane, 1.8 mL, 3.5 mmol) was then added dropwise. The solution
was stirred for 12 h, at which time the reaction was cooled to
-78 °C. A solution of 10 (873 mg, 1.59 mmol) in THF (1.6 mL)
was then added. The reaction was stirred for an additional 12
h at -78 °C. Saturated NH4Cl was added to quench the
reaction, and the mixture was diluted with ethyl acetate. The
solution was washed with brine. The organic layer was dried
over Na2SO4, filtered, and concentrated in vacuo to yield a
crude yellow oil. Flash column chromatography on silica gel
eluting with 15-25% EtOAc:hexanes afforded the dithioketal
11 as an off-white solid (566 mg, 52.5%): mp 83-85 °C. 1H

Generation of 2′-Deoxy-5-methyleneuridin-5-yl
J . Org. Chem., Vol. 65, No. 15, 2000 4653
NMR (CDCl3) δ: 8.49 (s, 1H), 7.49 (s, 1H), 7.33 (m, 5H), 6.36
(t, J ) 6.8 Hz, 1H), 4.44 (m, 1H), 3.93 (m, 1H), 3.74 (t, J ) 3
Hz, 2H), 3.31 (d, J ) 3.9 Hz, 2H), 2.91 (m, 6H), 2.34 (m, 1H),
2.08 (m, 1H), 0.93 (s, 9H), 0.89 (s, 9H), 0.114 (s, 3H), 0.107 (s,
3H), 0.06 (s, 3H), 0.03 (s, 3H). 13C NMR (CDCl3) δ: 163.5,
149.8, 139.0, 135.9, 131.3, 127.7, 126.9, 109.4, 87.4, 84.7, 71.8,
62.8, 54.7, 46.2, 0.7, 35.6, 26.4, 25.9, 25.7, 24.1, 18.3, 18.0, -4.7,
-4.9, -5.3, -5.5. IR (film): 2953, 2929, 2857, 682, 1463, 1254,
1103, 837 cm-1. Anal. Calcd for C33H54N2O5S2Si2: C, 58.34;
H, 6.54; N, 4.13. Found: C, 58.23; H, 6.22; N, 4.13.
(500 µL), and Et3N‚3HF (91 µL, 90.1 mg) were placed in a 10-
mL round-bottom flask and stirred for 24 h. After the solvents
were removed in vacuo, flash chromatography on silica gel
eluting with 5-10% MeOH/EtOAc afforded 13 as a white solid
(18.8 mg, 96%): mp 164-166 °C. 1H NMR (CD3OD) δ: 7.79
(s, 0.6H), 7.76 (s, 0.4H), 7.23 (m, 5H), 6.26 (m, 1H), 4.39 (m,
1H), 4.02 (m, 1H), 3.90 (m, 1H), 3.77 (dd, J ) 2.7, 9.3 Hz, 1H),
3.72 (J ) 2.7, 9.3 Hz, 1H), 2.77 (m, 2H), 2.60 (m, 1H), 2.32 (m,
1H), 2.26 (m, 2H). 13C NMR (CD3OD) δ: 166.3, 152.4, 140.4,
140.1, 140.0, 130.7, 129.4, 127.3, 112.7, 89.0, 86.5, 72.3, 71.8,
71.7, 63.0, 45.0, 41.4, 41.3, 36.0. IR (film): 3389, 2925, 1685,
1471, 1276, 1053 cm-1. HRMS (FAB): C18H22N2O6 calcd
(M+ + H) 363.1556, found 363.1563.
3′,5′-Bis-O-(ter t-bu tyld im eth ylsilyl)-5-(2-p h en yleth yl)-
2′-d eoxyu r id in e. 3′,5′-Bis-O-(tert-butyldimethylsilyl)-5-sty-
renyl-2′-deoxyuridine (16)22a (75 mg, 0.14 mmol), 10% palla-
dium on carbon (39.7 mg), and MeOH (16.9 mL) were placed
in a 100-mL hydrogenation chamber. The chamber was pres-
surized with hydrogen gas (40 psi) and allowed to stir
overnight. The reaction mixture was filtered through Celite,
and the solvent was removed in vacuo. Flash chromatography
on silica gel eluting with 33-100% EtOAc:hexanes afforded
the reduced compound as a light yellow oil (44.7 mg, 59.2%).
1H NMR (CDCl3) δ: 8.83 (bs, 1H), 7.24 (m, 5H), 6.30 (dd, J )
5.7, 2.1 Hz, 1H), 4.34 (m, 1H), 3.89 (m, 1H), 3.73 (t, J ) 3.6,
2H), 2.85 (m, 2H), 2.63 (m, 2H), 2.19 (m, 1H), 1.82 (m, 1H),
0.93 (s, 9H), 0.91 (s, 9H), 0.11 (s, 6H), 0.09 (s, 6H). 13C NMR
(CDCl3) δ: 163.4, 150.4, 141.4, 136.2, 128.9, 128.6, 126.2, 114.2,
87.8, 84.8, 72.3, 63.1, 41.2, 35.0, 29.8, 26.2, 26.1, 26.0, 18.6,
18.2, -4.4, -4.6, -5.1, -5.2. IR (film): 2953, 2929, 2857, 1696,
1463, 1254, 1101, 1030, 835 cm-1. HRMS (FAB): C29H48N2O5-
Si2 calcd (M+ + H) 561.3180, found 561.3188.
3′,5′-Bis-O-(ter t-bu tyld im eth ylsilyl)-5-(3-p h en yl-2-oxo-
p r op yl)-2′-d eoxyu r id in e (12). Mercuric chloride (544 mg, 2.0
mmol), CaCO3 (216 mg, 2.17 mmol), and 4:1 CH3CN:H2O (8.3
mL) were added to a 50-mL round-bottom flask containing 11
(566 mg, 0.83 mmol). The white slurry was heated at reflux
for 8 h. The solution was allowed to cool to room temperature,
and the condenser was rinsed with CH2Cl2. The reaction
mixture was then filtered through Celite and rinsed with CH2-
Cl2 to remove mercury salts and CaCO3. The filtrate was
washed with H2O, dried over Na2SO4, filtered, and concen-
trated in vacuo to yield a crude white solid. Flash column
chromatography on silica gel eluting with 10-20% EtOAc:CH2-
Cl2 afforded 12 as a white foam (365 mg, 92%): mp 62-63 °C
1
(shrinks), 65-67 °C (glass). H NMR (CDCl3) δ: 9.79 (s, 1H),
7.50 (s, 1H), 7.30 (m, 5H), 6.36 (dd, J ) 6, 1.8 Hz, 1H), 4.39
(m, 1H), 3.93 (m, 1H), 3.85 (s, 2H), 3.82 (dd, J ) 3, 11.4 Hz),
3.74 (dd, J ) 3, 11.4 Hz), 3.52 (d, J ) 17.1 Hz, 1H), 3.32 (d,
J ) 17.1 Hz, 1H), 2.28 (m, 1H), 2.03 (m, 1H), 0.91 (s, 9H),
0.88 (s, 9H), 0.10 (s, 3H), 0.09 (s, 3H), 0.06 (s, 3H), 0.04 (s,
3H). 13C NMR (CDCl3) δ: 204.2, 163.1, 150.2, 138.4, 134.0,
129.7, 128.9, 127.3, 108.6, 88.0, 85.3, 72.4, 63.1, 50.2, 41.5, 39.4,
26.1, 26.1, 25.9, 18.5, 18.2, -4.5, -4.7, -5.3. IR (film): 2954,
2857, 1688, 1471, 1255, 1097, 1031, 837, 778 cm-1. HRMS
(FAB): C30H48N2O6Si2 calcd (M+ + H) 589.3129, found 589.3134.
5-(1-(3-P h en yl-2-oxop r op yl))-2′-d eoxyu r id in e (7). To a
50-mL round-bottom flask containing 12 (360 mg, 0.76 mmol)
were added THF (7.6 mL) and Et3N‚3HF (1.24 mL, 1.23 g, 7.6
mmol). The reaction was stirred for 10 h at room temperature.
The solvents were removed in vacuo by rotary evaporation.
Flash chromatography on silica gel eluting with 10-20%
MeOH:EtOAc afforded deprotected ketone as a white solid (204
mg, 74%): mp 163-165 °C. 1H NMR (CD3OD) δ: 7.82 (s, 1H),
7.25 (m, 5H), 6.26 (t, J ) 6.8, 1H), 4.38 (m, 1H), 3.89 (m, 1H),
3.86 (s, 2H), 3.73 (dd, J ) 3.3, 9.6 Hz, 2H), 3.48 (d, J ) 6.6
Hz, 2H), 2.21 (m, 2H). 13C NMR (CD3OD) δ: 207.6, 152.3,
140.7, 135.8, 130.9, 129.7, 128.1, 110.0, 89.0, 86.6, 72.2, 62.9,
50.3, 50.0, 41.5, 40.8. IR (film): 3366, 1682, 1470, 1275, 1091,
1056. HRMS (FAB): C18H20N2O6 calcd (M + 1) 361.1400, found
361.1406.
5-(2-P h en yleth yl)-2′-d eoxyu r id in e (14).22b 3′,5′-Bis-O-
(tert-butyldimethylsilyl)-5-(2-phenylethyl)-2′-deoxyuridine (44.7
mg, 80 µmol), Et3N‚3HF (13 µL, 13 mg, 0.8 mmol), and THF
(0.8 mL) were placed in a 25-mL pear-shaped flask. The
reaction was allowed to stir for 24 h, at which time the solvents
were removed in vacuo. Flash column chromatography on
silica gel eluting with 19:1 EtOAc:MeOH (50 mL) afforded 14
as a white solid (23 mg, 90%). 1H NMR (CDCl3) δ: 7.51 (s,
1H), 7.17 (m, 5H), 6.2 (t, J ) 6.9, 1H), 4.24 (m, 1H), 3.82 (dd,
J ) 3.3, 6.6 Hz, 1H), 3.63 (qd, J ) 12, 3.3 Hz, 2H), 2.73 (m,
3H), 2.50 (m, 1H), 2.11 (m, 1H), 1.92 (m, 1H).
5-Eth a n a l-2′-d eoxyu r id in e (15). THF (800 µL) and Et3N‚
3HF (134 µL, 133 mg, 0.82 mmol) were added to a 25-mL
round-bottom flask containing 1723 (41 mg, 82 µmol). The
reaction was allowed to stir for 10 h at room temperature, at
which time the solvents were removed in vacuo. Flash chro-
matography on silica gel eluting with 10-20% MeOH:EtOAc
1
3′,5′-Bis-O-(ter t-b u t yld im et h ylsilyl)-5-(1-(3-p h en yl-2-
h yd r oxyp r op yl))-2′-d eoxyu r id in e. Ethanol (500 µL) was
added to a 10-mL pear-shaped flask containing 12 (21.3 mg,
36.2 µmol). The solution was cooled to 0 °C, and NaBH4 (1.4
mg, 36.2 µmol) was then added. The reaction was allowed to
stir for 12 h while warming to room temperature. The reaction
was quenched with H2O and washed with CH2Cl2 and H2O.
The aqueous layer was extracted with CH2Cl2. The organic
layers were combined, dried over Na2SO4, filtered, and con-
centrated in vacuo to yield a clear glass. Flash column
chromatography on silica gel eluting with 4:1 CH2Cl2:EtOAc
(75 mL) afforded the bis-TBDMS-protected alcohol (21.3 mg,
afforded 15 as a clear glass (16.4 mg, 74%). H NMR (D2O) δ:
9.60 (s, 0.3 H), 7.68 (s, 1H), 6.23 (t, J ) 7 Hz, 1H), 5.18 (t,
J ) 5 Hz, 1H), 4.41 (m, 1H), 3.98 (m, 1H), 3.77 (m, 2H), 2.57
1
(d, 1H), 2.38 (m, 2H). H NMR (CD3OD) δ: 7.80 (d, 1H), 6.27
(t, J ) 7 Hz, 1H), 4.74 (t, J ) 5 Hz, 1H), 4.39 (m, 1H), 3.91 (m,
1H), 3.75 (dd, 2H), 3.36 (s, 3H), 2.55 (m, 2H), 2.23 (m, 2H). IR
(film): 3374, 2928, 1682, 1471, 1276, 1094, 1052 cm-1. LRMS
(FAB): C11H14N2O6 calcd 289.3 (M+ + H), found 289.1.
3′,5′-Di-(ter t-bu tyld im eth ylsilyl)-5-(3,3′-d im eth yl-2-oxo-
bu tyl)-2′-d eoxyu r id in e (9). To a solution of the protected 2′-
deoxyuridine (0.25 g, 0.55 mmol) in THF (20 mL) was added
TMEDA (0.16 g, 1.37 mmol), followed by s-BuLi (1.05 mL of
1.3 M in cyclohexane, 1.37 mmol) at -78 °C. After 1 h of
stirring at -78 °C, 1-bromopinacolone (0.49 g, 2.74 mmol) in
THF (3 mL) was added to the reaction mixture which was
allowed to warm to room temperature. The reaction mixture
was quenched with saturated NH4Cl solution, followed by H2O.
The aqueous layer was extracted with EtOAc. The combined
organic layers were washed with water, brine, dried over Na2-
SO4, and then evaporated under reduced pressure to give a
brown oil. Flash chromatography (eluent; hexanes:ether, 3:1)
1
99.5%) as a 2:1 mixture of diastereomers: mp 50-53 °C. H
NMR (CDCl3) δ: 8.54 (bs, 1H), 7.50 (s, 0.6H) 7.44 (s, 0.4H),
7.28 (m, 5H), 6.30 (m, 1H), 4.39 (m, 1H), 4.03 (bs, 1H), 3.93
(m, 1H), 3.81 (dd, J ) 3, 11.4 Hz, 1H), 3.73 (dd, J ) 3, 11.4
Hz, 1H), 2.80-2.62 (m, 4H), 2.43 (m, 1H), 2.25 (m, 1H), 2.00
(m, 1H), 0.90 (s, 18H), 0.08 (s, 12H). 13C NMR (CDCl3) δ: 164.7,
164.4, 150.1, 150.0, 138.4, 138.4, 138.1, 138.0, 129.7, 128.7,
126.7, 112.0, 111.9, 88.2, 88.0, 85.5, 85.2, 72.7, 72.4, 71.8, 71.5,
63.3, 63.2, 44.2, 44.1, 41.5, 41.3, 35.3, 35.0, 26.1, 26.0, 18.6,
18.2, -4.4, -4.6, -5.1, -5.2. IR (film): 3185, 2953, 1711, 1471,
1116, 1062, 836 cm-1. HRMS (FAB): C30H50N2O6Si2 calcd
(M+ + H) 591.3286, found 591.3284.
1
yielded 9 (60 mg, 20%) as a pale brown oil. H NMR (CDCl3)
δ: 8.08 (s, 1H), 6.26 (dd, J ) 5.7, 7.5 Hz, 1H), 4.91 (s, 2H),
4.36 (m, 1H), 3.95 (q, J ) 2.2 Hz, 1H), 3.87 (dd, J ) 2.8, 11.6
Hz, 1H), 3.74 (dd, J ) 2.2, 11.6 Hz, 1H), 2.29 (ddd, J ) 2.6,
5.7, 13.1 Hz, 1H), 2.00 (m, 1H), 1.23 (s, 9H), 0.91 (s, 9H), 0.86
5-(1-(3-P h en yl-2-h yd r oxyp r op yl))-2′-d eoxyu r id in e (13).
The bis-O-TBDMS-protected alcohol (33 mg, 55.9 µmol), THF

4654 J . Org. Chem., Vol. 65, No. 15, 2000
Anderson et al.
(s, 9H), 0.12 (d, J ) 2.9 Hz, 6H), 0.05 (s, 6H). 13C NMR (CDCl3)
δ: 206.8, 158.7, 150.0, 138.0, 96.4, 88.6, 86.7, 72.5, 63.2, 46.8,
43.6, 42.3, 26.5, 26.3, 26.0, 18.8, 18.3, -4.30, -4.6, -5.0, -5.1.
IR (film): 2955, 2930, 2858, 1714, 1669, 1447, 1257, 1112,
Ack n ow led gm en t. We are grateful for financial
support of this research from the National Institutes of
Health (GM-54996) and for a fellowship from the Alfred
P. Sloan Foundation to M.M.G. Mass spectra were
obtained on instruments supported by the National
Institutes of Health shared instrumentation grant GM-
49631.
1071, 836 cm-1. HRMS (FAB): calcd for C27H51N2O6Si2 (M+
H) 555.3286; found 555.3296.
+
5-(3,3′-Dim eth yl-2-oxobu tyl)-2′-d eoxyu r id in e (6). To a
solution of 9 (50 mg, 0.08 mmol) in anhydrous methanol (10
mL) was added NH4F (26 mg, 0.73 mmol). The reaction
mixture was heated at 55-60 °C for 27 h. After the solvent
was removed under reduced pressure, the residue was purified
by flash chromatography (eluent; CH2Cl2:MeOH, 20:1 to 10:
Su p p or tin g In for m a tion Ava ila ble: HPLC retention
times and response factors versus 2′-deoxyuridine for thymi-
dine, 7, and 13-15. Ratio of protio versus deuterio tert-
butylthiol as a function of H2O:D2O ratio. Tabulated data for
competition for 1 between recombination and hydrogen atom
donation from 2,5-dimethyltetrahydrofuran and propan-2-ol.
Plot of recombination product 14 yield versus extent deutera-
tion of tert-butylthiol. This material is available free of charge
via the Internet at http://pubs.acs.org.
1
1) to yield 6 (24 mg, 85%) as a white foam. H NMR (CD3OD)
δ: 8.59 (s, 1H), 6.21 (t, J ) 6.6 Hz, 1H), 4.97 (s, 2H), 4.40 (m,
1H), 3.94 (q, J ) 3.0 Hz, 1H), 3.83 (dd, J ) 3.0, 12.3 Hz, 1H),
3.73 (dd, J ) 3.0, 12.0 Hz, 1H), 2.37-2.19 (m, 2H), 1.24 (s,
9H). 13C NMR (CD3OD) δ: 209.6, 160.7, 151.4, 141.0, 136.1,
96.2, 89.4, 88.2,71.8, 62.4, 48.1, 44.5, 42.1, 26.7 (3C). IR
(film): 3450 (br), 2954, 1708, 1658, 1449, 1267, 1213, 1096,
1073 cm-1
.
J O000271S