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T
he 3'-
N-sulfamate analogue of t
hymidylyl(3'-5')t
hymidine (TnsoT,
1) ex
hibits a preference for a C3'-endo conformation in t
he solution and solid states. Its p
hotoc
hemical be
havior in solution is comparedto t
hat of its natural counterpart, t
hymidylyl(3'-5')t
hymidine (TpT,
2), to get furt
her insig
ht into t
hesignificance of t
he C3'-endo conformation on t
he p
hotoproduct formation at t
he single-stranded dinucleotidelevel. Irradiation at 254 nm of
1 led to t
he same type of p
hotoproducts as observed wit
h 2. However,
1was significantly more p
hotoreactive t
han
2, and accordingly, t
he initial rate of p
hotoproduct formationwas en
hanced in accordance wit
h its propensity to base stack compared to
2. T
he corresponding quantumyields were determined and s
howed t
hat t
he en
hancement factor (
1 compared to
2) is moderate for t
hecyclobutane pyrimidine dimer (CPD) (1.26) and muc
h hig
her for t
he (6-4) p
hotoproduct (1.8). T
hesedata strongly suggest t
hat t
he CPD and (6-4) p
hotoproduct arise from distinct minor stacked conformations.