Biomedical subjects
Publications and source records attributed to Patrick H Dussault.
[Structure: see text] Ozonolysis of alkenes in the presence of amine N-oxides results in the direct formation of aldehydes. This reaction, which appears to involve an unprecedented trapping and fragmentation of the short-lived carbonyl oxide intermediates, avoids the hazards associated with generation and isolation of ozonides or other peroxide products.
The first asymmetric synthesis of 1,2-dioxolane-3-acetic acids is reported. Key features include the stereoselective opening of enantiomerically enriched oxetanes by hydrogen peroxide, conversion of the resulting 4-hydroperoxy-2-alkanols to 3-alkoxy-1,2-dioxolanes, and Lewis acid mediated homologation of the latter with a thioester silyl ketene acetal. The approach is modeled on 3,5-dimethyl-5-hexadecyl-1,2-dioxolane-3-acetic acid (1a), an unnamed natural product, and an optimized strategy is applied to the synthesis of four stereoisomers of plakinic acid A (2), allowing a configurational assignment of this incompletely characterized natural product.
Fumonisins are a group of polyketide-derived mycotoxins produced by Fusarium verticillioides, a filamentous fungus infecting corn and contaminating food and feeds. Fumonisins contain two tricarballylic esters that are critical for toxicity. Here, we present genetic and biochemical data for the esterification mechanism. FUM14 in F. verticillioides has been deleted by homologous recombination, and the resultant mutant lost the ability to produce fumonisins. Two new metabolites, HFB(3) and HFB(4), which are biosynthetic precursors of fumonisins lacking the tricarballylic esters, were detected in the mutant. The results suggest that FUM14 is required for the esterification of fumonisins. FUM14 was predicted to encode a nonribosomal peptide synthetase (NRPS) containing two domains, peptidyl carrier protein and condensation domain. Both the intact Fum14p and the condensation domain have been expressed in Escherichia coli and purified for activity assays. Fum14p was able to convert HFB(3) and HFB(4) to the tricarballylic esters-containing fumonisins, FB(3) and FB(4), respectively, when incubated with tricarballylic thioester of N-acetylcysteamine. In addition, the condensation domain was able to convert HFB(1) to FB(1). These data provide direct evidence for the role of Fum14p in the esterification of fumonisins. More interestingly, the results are the first example of an NRPS condensation domain catalyzing a C-O bond (ester) formation, instead of the typical C-N bond (amide) formation in nonribosomal peptides. The understanding of the esterification mechanism provides useful knowledge for mycotoxin reduction and elimination. The study also provides new insight into the reactions catalyzed by NRPS.
Consumption of plant sterol esters reduces plasma LDL cholesterol concentration by inhibiting intestinal cholesterol absorption. Commercially available plant sterol esters are prepared by esterifying free sterols to fatty acids from edible plant oils such as canola, soybean, and sunflower. To determine the influence of the fatty acid moiety on cholesterol metabolism, plant sterol esters were made with fatty acids from soybean oil (SO), beef tallow (BT), or purified stearic acid (SA) and fed to male hamsters for 4 wk. A control group fed no plant sterol esters was also included. Hamsters fed BT and SA had significantly lower cholesterol absorption and decreased concentrations of plasma non-HDL cholesterol and liver esterified cholesterol, and significantly greater fecal sterol excretion than SO and control hamsters. Cholesterol absorption was lowest in hamsters fed SA (7.5%), whereas it was 72.9% in control hamsters. Cholesterol absorption was correlated with fecal sterol excretion (r = -0.72, P < 0.001), liver cholesterol concentration (r = 0.88, P < 0.001), and plasma non-HDL cholesterol concentration (r = 0.85, P < 0.001). A multiple regression model that included each sterol ester type vs. cholesterol absorption indicated that intake of steryl stearate was the only dietary component that contributed significantly to the model (R2 = -0.75, P < 0.001). Therefore, our results demonstrate that BT and SA are more effective than SO in reducing cholesterol absorption, liver cholesterol, and plasma non-HDL cholesterol concentration, suggesting that cardioprotective benefits can be achieved by consuming stearate-enriched plant sterol esters.
[reactions: see text] The 5-exo openings of oxetanes by hydroperoxides proceed rapidly and stereospecifically to furnish 1,2-dioxolanes. The corresponding 6-exo cyclizations are slower and proceed with moderate stereoselectivity. In the case of hydroperoxy acetals, 5-exo nucleophilic transfer of alkoxide competes effectively with 6-exo attack by the hydroperoxide.
[reaction: see text] The first syntheses of peroxyacarnoates A and D, members of a family of enyne-containing alkoxydioxanes, have been achieved on the basis of chemoselective ozonolysis within a polyunsaturated framework and Pd-mediated cross-couplings of a functionalized 1,2-dioxane.
We describe ten polyene analogs of farnesol, typified by 3,7,11-trimethyl-2,4,6,8,10-dodecapentenaldehyde oxime, which preserve the length, cross-section, and approximate hydrophobicity of farnesol. Four of the ten display strong quorum-sensing activity in the human pathogen Candida albicans, with IC(50) values for inhibition of germ-tube formation as low as 10 microM. The polyenes display absorption maxima between 320 and 380 nm, with the extinction coefficients for the oximes approaching 100,000. All but two of the analogs are fluorescent, with excitation maxima varying over the range of 320-370 nm. Oxime anti-4, which can undergo fluorescence excitation at wavelengths beyond 400 nm, is demonstrated to be useful for confocal fluorescence microscopic imaging of fungal cells. The farnesol analogs are also expected to be useful for detection of farnesol binding proteins and in determination of farnesol pharmacokinetics.
[reaction: see text] 1,2,4-trioxepanes, readily prepared and easily handled derivatives of aldehydes and ketones, are stable to a variety of synthetic conditions and yet easily deblocked with Zn/HOAc or Mg/MeOH to regenerate the parent carbonyl. Trioxepanes may provide an alternative to 1,3-dithianes for acid-stable protection of carbonyl groups.
Magnesium in methanol is an effective reagent for the chemoselective reduction of peroxides, including ozonides. Mg/MeOH is significantly more reactive than Me(2)S or PPh(3) and somewhat more reactive than Zn/HOAc.
The first asymmetric syntheses of the cutin monomers (R)- and (S)-10,16-dihydroxyhexadecanoic acid (10,16-DHPA) and confirmation of (S)(+)-absolute configuration for 10,16-DHPA derived from tomato are reported. The individual DHPA stereoisomers display differences in their ability to activate the fungal pathogen Colletotrichum trifolii.
[reaction: see text] Lewis acid-catalyzed opening of oxetanes by hydrogen peroxide proceeds regioselectively and with good to moderate stereoselectivity to furnish enantiomerically enriched 3-hydroperoxyalkanols. The corresponding opening using alkyl hydroperoxides furnishes 3-peroxyalkanols. The hydroperoxyalkanols are easily converted into enantiomerically enriched 1,2,4-trioxepanes, building blocks for antimalarials.