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ChemComm
DOI: 10.1039/C5CC03312H
peak at m/z 580.1735 (Figure S38A in ESI†) in the HRMS of the
1.
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reaction mixture, after 20 min of stirring, allowed us to propose
the formation of species 12. Due to the overlapping with NADH
signals, it was difficult to see uracilC5ꢀCH3 signal of species 12
in the 1H NMR spectrum. No further change was observed in the
reaction (2h) and due to low yield; 12 was not isolated.
Alternatively, 11 was converted to 13 by changing the pH of the
reaction mixture to 9.5 (Figure S38B, S39 in ESI†).
Subsequently, addition of NADH to the reaction mixture (pH 7.0)
10 furnished thymine (82%) (Scheme 1b, Figure S38C, S40, S41 in
ESI†) and compound 15 (80%, Scheme 1b, Figure S42 in ESI†).
Probably, the carboxyl group has provided Hꢀbond activation to
the Sꢀbridge and either through route A or B, thymine was made
free from compound 13. Supporting this mode of conversion of
15 13 to 15 and thymine, no change was observed at pH 9.5 which
was probably due to the presence of carboxylate (COOꢀ) ion at
this pH and hence no Hꢀbond with Sꢀbridge. More evidences are
given in the ESI† (Figure S43, Figure S44, Scheme S5).
70
5
75 4.
5.
80 6.
7.
85 8.
9.
The proposed mechanism in Scheme 1b was supported by the
20 isolation of thymineꢀ13CH3 (73%, Scheme S6, Figure S45) and
compound 20 (70%, Figure S46) from the reaction of 1d-13Cepox
(prepared by using 13C labelled epichlorohydrin) with uracil.
Typically, a doublet signal for 13CH3 group (J1Hꢀ13C = 65 Hz) is
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1
1
visible in the H NMR spectrum of thymine. Comparison of H
25 NMR spectrum of 20 and 15 (Figure S46d in ESI†) clearly
showed a difference in the splitting pattern of CH2=CHꢀ
hydrogens. 13C–1H Coupling was apparent from the multiplicity
90
1
of these three signals in the H NMR spectrum of 20. Evidently,
12.
B. Hong, F. Maley, A. Kohen, Biochemistry 2007, 46, 14188 –
one of the three Cs′ of oxiranmethyl unit was transferred to uracil
30 and the other two Cs′ remain with compound 15/20. None of the
nucleobases amongst cytosine, thymine, 5ꢀhydroxymethyluracil,
5ꢀfluorouracil, adenine and guanine reacted chemically with
compound 1d under the current reaction conditions though the
peak corresponding to the additive mass of the nucleobase and 1d
35 was detected in the ESIꢀHRMS of the reaction mixture.
95
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In conclusion, the present study illuminates a model reaction
designed via inspiration from TSase catalysis for dUMP
conversion to dTMP. To the best of our knowledge (Table S1),
this is the first report of a pH driven biomodel reagent in which
40 all the steps A – E (Scheme 1a) of TSase catalyzed reaction are
mimicked. In particular, the key species 7, 8, 9, 11 and thymine
which correspond to the steps B, C, D and E of TSase catalyzed
reaction, were either isolated or spectrophotometrically detected.
This chemical parallelism would be most instrumental in further
45 investigation of TSase mechanism. Beyond the interesting
chemistry, it may add insights to mechanism based drug design
targeting TSase. Further refining of the biomodel to achieve the
conversion of dUMP to dTMP, determining the kinetics of
various steps of the reaction and testing of other relevant reducing
50 agents like tetrahydrobiopterin for the conversion of exocyclic
methylene to methyl group are underway so that a true substitute
of TSase is developed
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Financial assistance by DST, and CSIR, New Delhi is
gratefully acknowledged. AK and SK thanks CSIR, New Delhi
55 and AS thanks DST, New Delhi for fellowship. Thanks are due to
Prof. R. C. F. Jones for fruitful suggestions. Authors thank Prof.
A. S. Brar, ViceꢀChancellor, GNDU for creating state of the art
research facilities under the UPE programme of UGC.
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60 aDepartment of Chemistry, UGC Sponsored Centre for Advanced Studies,
Guru Nanak Dev University, Amritsar-143005. India.
Fax: 91 183-2258819; Tel: 91 183 2258802 x 3495;
†Electronic Supplementary Information (ESI) available: [General
65 procedure, mass spectra, NMR spectra]. See DOI: 10.1039/b000000x/
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