- Enantioselective synthesis of: Iboga alkaloids and vinblastine via rearrangements of quaternary ammoniums
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An efficient and novel strategy for the enantioselective syntheses of various iboga alkaloids has been developed. The salient features include a gold-catalyzed oxidation of a terminal alkyne followed by cyclization, a Stevens rearrangement and a tandem sequence that combines the gold-catalyzed oxidation, cyclization and [1,2]-shift. The catharanthine analogs provided by our approach were further converted to the vinca alkaloid vinblastine and its analogs, which confirmed the remarkable sensitivity of the cytotoxicity to the C20′ substituent of vinblastine.
- Zhang, Yun,Xue, Yibin,Li, Gang,Yuan, Haosen,Luo, Tuoping
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- Synthesis of (+)-vinblastine and its analogues
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(Chemical Equation Presented) A synthetic route to vinblastine and its analogues with an ethynyl group, which features a stereoselective coupling of an 11-membered key intermediate with vindoline, is described. Transformations of the alkynyl moiety including a partial reduction as well as a Sonogashira coupling furnished a variety of analogues.
- Miyazaki, Tohru,Yokoshima, Satoshi,Simizu, Siro,Osada, Hiroyuki,Tokuyama, Hidetoshi,Fukuyama, Tohru
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p. 4737 - 4740
(2008/03/15)
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- Methods for stabilizing biologically active agents encapsulated in biodegradable controlled-release polymers
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Methods for reducing or inhibiting the irreversible inactivation of water-soluble biologically active agents in biodegradable polymeric delivery systems which are designed to release such agents over a prolonged period of time, such as PLGA delivery systems are provided. The method comprises preparing a PLGA delivery systems whose microclimate, i.e. the pores where the active agent resides, uniformly or homogenously maintain a pH of between 3 and 9, preferably between 4 and 8, more preferably between 5 and 7.5 during biodegradation. Depending on the size of the delivery system, and the initial bulk permeability of the polymer, this result is achieved by (a) incorporating a water-soluble carrier into the delivery system, (b) incorporating a select basic additive (or antacid) into the delivery system, (c) incorporating both a water soluble carrier and a select basic additive into the delivery system, (d) adding a pore forming molecule for increasing the rate of release of low molecular weight monomers and oligomers into the delivery system, (e) using a PLGA polymer with reduced glycolide content, i.e. PLGA with from 100% to 75% lactide and 0 to 25% glycolide) (f) using a microencapsulation method that yields a more extensive pore-network, e.g. oil-in-oil emulsion-solvent extraction as opposed to water-in-oil-in water-solvent evaporation method, and (g) combinations thereof.
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