Pii: S0968-0896(99)00042-5
نویسندگان
چکیده
ÐUtilization of 17-keto-androstanes as starting materials for the synthesis of aor b-oriented steroidal 20!16-g-carbolactones has been explored following two dierent strategies. A highly ecient, stereospeci®c protocol has been developed for the boriented cis-g-lactone. A dierent approach, involving prior attachment of a 3-carbon side chain on C-17 of a 17-oxo-16b-acetoxyandrostane led to the epimeric, a-oriented lactone. The mechanism of the rearrangement of epimeric 16bor 16a-hydroxy-17-ketoandrostanes to 17b-hydroxy-16-keto-androstanes was studied by C NMR spectroscopy. The former occurs through a 1,2-sigmatropic H-shift, while the latter is likely to take place by simple enolization±reprotonation.# 1999 Elsevier Science Ltd. All rights reserved.
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Pii: S0968-0896(97)00137-5
-Philanthotoxins are noncompetitive inhibitors of the nicotinic acetylcholine receptor and the various glutamate r<.~ceptors. Analogues carrying photoaffinity labels, fluorine atoms for solid-state NMR studies of ligand/receptor interaction, and large head groups such as porphyrins and planar bulky aromatic rings (BIG analogues) for clarifying mode of entry and orientation of analogues in recep...
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ÐConjugates of bisphosphonates (potential bone resorption inhibitors) and prostaglandin E2 (a bone formation enhancer) were prepared and evaluated for their ability to bind to bone and to liberate, enzymatically, free PGE2. The conjugate 3, an amide at C-1 of PGE2 proved to be too stable in vivo while conjugate 6, a thioester, was too labile. Several PGE2, C-15 ester-linked conjugates (18, 23, ...
متن کاملPii: S0531-5565(99)00042-x
The genetics of aging in Drosophila are reviewed under the separate headings of population genetics, physiological genetics, and molecular genetics. However, connections between these sub-fields are brought forward for discussion. © 1999 Elsevier Science Inc. All rights reserved.
متن کاملPii: S0968-0896(98)00173-4
ÐA number of model compounds resembling the fundamental bonding patterns of residual kraft lignin, including a series of stilbenes, were incubated with laccase from Trametes versicolor in the presence and absence of deligni®cation `mediators' ABTS and HBT. The condensed kraft lignin model compounds seem to undergo initial degradation by laccase mainly via benzylic oxidation, demethylation and h...
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