The discovery of the methylerythritol phosphate pathway (the MEP pathway)
as an alternate pathway for isoprenoid biosynthesis in some organisms including
most bacteria, malarial parasites and plants, but not in animals, has stimulated
extensive studies in this area. Research has revealed the potential of finding novel
antibacterials, antimalarial drugs, and herbicides from enzyme inhibitors of this
pathway. The natural products fosmidomycin and FR900098 appear to be very
promising antibacterial and antimalarial compounds. Both compounds have
inhibition activities against the second enzyme in the MEP pathway, deoxyxylulose-
5-phosphate reductoisomerase (DXR), which mediates the conversion of
deoxyxylulose-5-phosphate (DXP) into methylerythritol-4-phosphate (MEP).
This thesis presents one aspect of the MEP pathway studies. Six different
analogs of DXP were designed based on the structural features of DXP to understand
the requirements of the DXR-substrate binding. Compounds with the trivial names
1-Me-DXP (containing an ethyl ketone moiety), DX-phosphonate (DXP having a
phosphonate group rather than a phosphate group), 4-epi-DXP (possessing the
opposite stereochemistry at the C��� position compared to DXP), 4-deoxy-DXP
(lacking the hydroxyl group at the C��� position), 3-deoxy-DXP (lacking the hydroxyl
group at the C��� position), and DXP carboxamide (having a primary amide group
rather than the methyl ketone) were synthesized and tested as alternate substrates and
enzyme inhibitors against DXR. The compound DX-phosphonate was the only
alternate substrate among the synthesized compounds. The remaining analogs of
DXP acted as weak competitive inhibitors against DXR. Kinetic studies of these
compounds provided an overall picture of how the substrate DXP binds to DXR.
Further studies of the compound 1-Me-DXP, using the published X-ray crystal
structures of DXR and DXR mutagenesis demonstrated more detail of the DXR
active site. The results present useful information for designing better enzyme
inhibitors.
The mechanism for the rearrangement of DXP to MEP by DXR was also
studied. Two possible mechanisms for this rearrangement have been proposed, the
��-ketol rearrangement and the retroaldol/aldol rearrangement. Several approaches
including the use of the potential alternate substrates, 4-deoxy-DXP and 3-deoxy-DXP were tried. Unfortunately none of the results obtained can definitively rule out
either of the mechanisms. Further studies are needed to completely understand this
mechanism and establish additional strategies for inhibition of DXR.
Syntheses of an intermediate from the DXR reaction, methylerythrose-4-phosphate, were also attempted in order to better understand the chemistry mediated
by DXR. Even though the target compound was not successfully obtained, several
synthetic approaches to this compound were useful for the syntheses of the different
DXP analogs mentioned above. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30901 |
| Date | 10 March 2004 |
| Creators | Phaosiri, Chanokporn |
| Contributors | Proteau, Philip J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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