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RM Williams

Publications and source records attributed to RM Williams.

6 recordsLinked to original sources
PubMed2000

Asymmetric, Stereocontrolled Total Synthesis of Paraherquamide A This work was supported by the NIH (Grant CA 70375). The Japanese Society for the Promotion of Science (JSPS) is acknowledged for providing support to H.T. Mass spectra were obtained on instruments supported by the NIH Shared Instrumentation Grant (GM 49631). We also wish to thank Dr. Timothy Blizzard (Merck & Co.) for providing an authentic sample of natural paraherquamide A. We also wish to acknowledge Dr. Byung H. Lee (Pharmacia-Upjohn Co.) for providing NMR spectra and an authentic specimen of 14-oxoparaherquamide B. We also wish to thank Dr. Alfredo Vazquez for assistance with purification and characterization of synthetic paraherquamide A.

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Journal Article↗
PubMed2000

Resolving SNR 0540-6944 from LMC X-1 with Chandra.

We examine the supernova remnant SNR 0540-697 in the Large Magellanic Cloud (LMC) using data from the Chandra Advanced CCD Imaging Spectrometer. The X-ray emission from this supernova remnant (SNR) had previously been hidden in the bright emission of the nearby X-ray binary LMC X-1; however, new observations with Chandra can finally reveal the SNR's structure and spectrum. We find the SNR to be a thick-shelled structure about 19 pc in diameter, with a brightened northeast region. Spectral results suggest a temperature of 0.31 keV and an X-ray luminosity (0.3-3.0 keV) of 8.4x1033 ergs s(-1). We estimate an age of 12,000-20,000 yr for this SNR, but note that this estimate does not take into account the possibility of cavity expansion or other environmental effects.

Journal Article↗
PubMed1999

Reductive Activation of a Hydroxylamine Hemiacetal Derivative of Dehydromonocrotaline: The First Reductively Activated Pyrrolizidine Alkaloid Capable of Cross-Linking DNA.

The acute hepatotoxicity displayed by the pyrrolizidine alkaloids, which obviates their clinical utility, is a result of activation in vivo by cytochrome P450 mediated oxidation. Now the first reductively activated progenitor of the highly cytotoxic dehydropyrrolizidine alkaloid dehydromonocrotaline has been synthesized and demonstrated to mediate interstrand DNA cross-link formation (see scheme); pyrrolizidine alkaloids exert their cytotoxicity through the formation of DNA-DNA interstrand and DNA-protein cross-links.

Journal Article↗