Chemistry Letters 2001
831
bonds as illustrated in Figure 3, where Zn(II)–OH– could locate
in a suitable position. It is worthy to note that such a complex
can be constructed with the CPK models without any difficulty.
In summary, we have demonstrated that a large rate accel-
eration for hydrolysis of the activated phosphodiester is
achieved by a cooperative effect of a metal ion and hydrogen
bonds by employing an H-bond-donor molecule bearing a
metal-binding site in MeCN. Such a molecule could be regard-
ed to exhibit an apoprotein function.
This work was supported in part by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan.
References and Note
1
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2
3
At [Zn(II)] / [melamine] = 2, kobs’s and relative rates are
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reactive species might be Zn(II)–OH–. Thus, effect of a base on
the rate was also examined. As can be seen in Table 1, addition
of a base such as 2,6-lutidine and 2,4,6-tris(diethylamino)-
1,3,5-s-triazine (5) accelerates the rates due to formation of
Zn(II)–OH–. The fact that 5 acts as a base indicates melamine
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four hydrogen bonds concern with stabilization of the transition
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4
5
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6
Although the structure of the ternary complex is not clari-
fied at present, the large rate acceleration for 2 and Zn(II)
allows us to propose that a trigonal bipyramidal and anionic
phospholane-like transition state is stabilized by four hydrogen
7
8
C. A. Bunton and S. J. Farber, J. Org. Chem., 34, 767 (1969).
The rate of hydrolysis of DPP– was negligible under the condi-
tions of Table 1.