Abstract:
This dissertation details the investigation of an alternate pathway to
isoprenoids that occurs in plants and microorganisms, the non-mevalonate
pathway. This exploration of the pathway focuses on the second step, the
conversion of 1-deoxy-D-xylulose-5-phosphate (DXP) to 2-C-methylerythritol-4-phosphate (MEP) by the enzyme DXP isomeroreductase (DXR). These studies led to an appreciation of the stereochemical course
of the enzymatic reduction step and to a better understanding of the
structural requirements for inhibitors to have optimal interactions at the
active site of the enzyme, DXR.
The investigation of the reduction step mediated by DXR revealed that
the C1 pro-S hydrogen in 2-C-methylerythritol-4-phosphate derives from C3
of DXP for the DXR from Synechocystis sp PCC6803. The pro-R hydrogen
originates from NADPH. The pro-S hydride of NADPH is transferred to the
re face of the proposed aldehyde intermediate, which designates DXR as a
class B dehydrogenase.
Based on the structural features of fosmidomycin, a known inhibitor of
DXR, several analogs were synthesized and evaluated for their inhibitory
activity against DXR. It was discovered that a polar head group with two
ionizable groups, a suitable length of intervening carbons, and an N-acyl N-hydroxy
moiety are important factors to demonstrate significant inhibition
activity. These studies also provided information that is complementary to
structural data obtained from recent X-ray crystal structures of DXR.
