Inhibitors chorismate mutase

Although chorismate mutase does provide a rate enhancement of 2 X 10 (147), this uni-molecular reaction readily occurs without enzyme, under mild conditions. The reaction was expected to pass through a chairlike transition state (59)(Fig. 17.25) but early molecular orbital calculations indicated that the boatlike transition state (60) was not out of the question (147). In an attempt to define the transition-state structure, several compounds, each designed to mimic a putative transition state, were synthesized and tested as chorismate mutase inhibitors (147). The enzyme was found to be inhibited by the exo-carboxy nonane (61), with an apparent value of 3.9 X 10 M Conversely, the endo-carboxy nonane (62) did not inhibit the enzyme. The apparent K- value of the adaman-... 

Use of chorismate mutase inhibitors to define the transition state structure. Biochemistry 16 4848-4852. 

In view of the varying behavior of chorismate mutases under different conditions and from different sources, we evaluated the best previously reported chorismate mutase inhibitor, 1-adamantyl phosphonate 35, in direct comparison with 41. Although the phosphonate... 

Andrews, P.R., Cain, E.N., Rizzardo, E. and Smith, G.D. (1977) Rearrangement of Chorismate to Prephenate. Use of Chorismate Mutase Inhibitors to Define the Transition State Structure, Biochemistry, 16,4848-4852. 

Bartlett, P.A., Nakagawa, Y., Johnson, C.R., Reich, S. and Luis, A. (1988) Chorismate Mutase Inhibitors Synthesis and Evaluation of Some Potential Transition State Analogs, J. Org. Chem., 53, 3195-3210. 

Wendt, S. McCombie, G. Daniel, J. Kienhofer, A. Hilvert, D. Zenobi, R. Quantitative evaluation of noncovalent chorismate mutase—inhibitor binding by Esi-Ms. J. Am. Soc. Mass Spectrom. 2003,14, 1470-1476. 

Adamantane has an extra methylene bridge (the asterisk in the diagram) linked to the six-membered ring, thus stabilizing a cagelike structure. The authors indeed subsequently showed that some adamantane derivatives are potent inhibitors of chorismate mutase thus, these are examples of transition-state analogs. 

The transition state for the enzymatic reaction has been shown to have a chairlike geometry as well [61], and conformationally constrained compounds that mimic this structure, such as the oxabicyclic dicarboxylic acid 1 (Fig. 3.6), are good inhibitors of chorismate mutase enzymes [62 - 64], How a protein might stabilize this high-energy species has been a matter of some debate. Recently, heavy atom isotope effects were used to characterize the structure of the transition state bound to BsCM [65]. A very... 

Fig. 3.6. Chorismate prefers a pseudodiequatorial conformation in solution. It must adopt a disfavored pseudodiaxial conformation to reach the pericyclic transition state. The conformationally constrained oxabicyclic dicarboxylic acid 1, which mimics the transition state, is a potent inhibitor of natural chorismate mutases [62], Antibodies raised against this compound also catalyze the reaction, albeit 100 to 10,000-times less efficiently than their natural counterparts [39, 41].

COMT is, for many of the same reasons as with chorismate mutase, well suited for the study with computational techniques. The reaction mechanism it catalyzes is the same mechanism that operates in the absence of the enzyme, specifically, the S 2 mechanism, facilitating comparison of the bare solution-phase reaction with the catalyzed reaction. The subsfiate and cofactor do not covalendy bind to the enzyme, so that defining the QM region and the MM region should be relatively uncomplicated. Lasdy, the X-ray crystal structure of COMT bound with the inhibitor 3,5-dinitrocatechol has been determined with a resolution of 2 kP An interesting twist to this enzyme is that the active site includes a metal cation, Mg " ". This crystal structure allows for a natural starting point for computational exploration of the means of the catalytic action of COMT. The rate acceleration provided by COMT is substantial the reaction is 10 times faster within the enzyme than in solution. " ... 

It has been shown that both the catalyzed and the uncatalyzed reaction proceed through a chairlike transition state, stabilized in polar media59 60-143 262-263. Compound 1, an analog of the transition-state structure, proved to be a potent inhibitor of E. coli chorismate mutase-prephenate dehydrogenase204-255. For a discussion of the mechanism and structural requirements of the enzyme see refs 266 and 267. 

Enzymatic studies with chorismate mutase prephenate dehydrogenase from Escherichia coli show that the chorismate prephenate analog 7 is not a substrate for chorismate mutase65. Both 7 and 8 are moderately competitive inhibitors for chorismate mutase. Ester derivatives 4 and 5, as well as 6, readily undergo Claisen rearrangements in organic solvents. 

Of the enzymes subsequent to EPSP synthase, only chorismate mutase has been the subject of inhibitor studies (see Chapter 5 by P. Bartlett in this volume). 

---