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Figure 13<br />

Two-dimensional structures of 2'-deoxy-2'-(3-methoxybenzamido)<br />

adenosine (MMBA), a selective T.brucei GAPDH inhibitor and<br />

MDL 73811, an irreversible<br />

inhibitor of trypanosomal S-adenosyl<br />

methionine decarboxylase.<br />

Page 387<br />

Finally, we want to point out that pessimism about adenosine derivatives as drugs is not necessarily<br />

warranted. This doubt stems from the argument that many proteins recognize NAD(P), adenosine, or<br />

ATP. Cross-reactivity of adenosine with these different proteins and, therefore, toxicity may be<br />

expected. That this is not necessarily so is evident from the use of adenosine derivatives as antileukemia<br />

agents. For example, fludarabine, a C2'-epimer of adenosine, exhibits relatively low toxicity [92]. The<br />

much bigger changes to the adenosine scaffold in our inhibitors may hence lead to a surprisingly high<br />

overall selectivity.<br />

V. Conclusions<br />

Our goal is to discover and design selective inhibitors of trypanosomal glycolsysis. Thusfar, three<br />

enzymes have been targeted. Whereas little success was obtained with TIM, substantial progress is being<br />

made with GAPDH and PGK.<br />

Obstacles encountered during this project were the need for selective inhibitors and the absence of<br />

potent inhibitors as lead compounds. From our studies to inhibit TIM it appears that it is difficult to<br />

come up with inhibitors for areas on the protein surface for which no known inhibitors exist. On the<br />

other hand, lead optimization for GAPDH <strong>by</strong> over two orders of magnitude in just one cycle of drug<br />

design was straightforward. Selectivity was obtained <strong>by</strong> using part of the cofactor as a lead and<br />

exploiting the hydrophobic patches at the surface of the parasite enzyme. In particular, 2'-deoxy-2' (3methoxy-benzamido)ade-<br />

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