Epoxides structure

Chen, Y., Puskas, J.E., and Tomkins, M. Investigation of the effect of epoxide structure on the initiation efficiency in isobutylene pol3mierizations initiated by epoxide/TiCLt systems, Eur. Polym. J., 39, 2147-2153, 2003. 

Diol epoxides. Structural considerations. Because enzymatic hydration of arene oxides produces trans dihydrodiols in mammalian cells, there are two diastereomeric series of diol epoxides. In... 

Different isomers of C qO have been prepared by photooxygenation [48], by MCPBA-oxidation [48], by ozonolysis [49] or they were extracted from fullerene soot [11, 50]. Isolation from fullerene soot and analysis of the product of photooxygenation and thermal ozonolysis yields only [6,6]-closed epoxide structures. As already observed for CgoO, ozonolysis and subsequent photolysis of the ozonide C7QO3 gives different [5,6]-open oxidoannulene structures [49]. 

Scarce resources, such as food or space, in some marine environments can lead to production of compounds for the offensive role of reducing competition. Focardin (Structure 7.171) and its 11,12-epoxide (Structure 7.172), produced by the Antarctic ciliate Euplotes focardii, are autotoxic and cytotoxic toward a sympatric ciliate and a selection of temperate and tropical predatory ciliates.195... 

WS009 A (220, = FR 901366) and B (221, = FR 901367), isolated from Strep-tomyces sp. No. 89009, were discovered during a screening course for endothelin receptor antagonists using ET-1, the most potent vasoconstrictor to date [160-162]. These compounds show a selective activity in an endothelin binding assay (IC50 5.8 x 10 M and 6.7 x 10" M, respectively). The structures feature a unique C-6 a linked N-acetylcysteine moiety which may have arisen biosyn-thetically via an attack of cysteine on a 6a -12 a epoxide structure, such as exemplified in A-683 (210) or SF 2315 B or elmycin C [3]. 

One novel compound 228 (Scheme 53), here designated WP 3688-3, from the PD 116198 (218) producer StreptomycesphaeochromogenesWP 3688 [159], (see also above and below) exhibits a 4a,12b epoxide structure and thus is another new prototype of an angucyclinone with oxygen at the ring AB fusion. The related structure 228 shows that all hydroxy residues of this oxygen-rich compound face the same direction 228 shows weak antibacterial activities. 

An investigation has been made of the stereochemistry of epoxidation of the sesquiterpene isolongifolene. The a-epoxide structure 29 has been proved by x-ray crystallography. 

The effects of epoxide structure on rates and product distributions indicate that LiC104 reactions occur by a carbenium ion mechanism. Conversely, the LiBr-catalyzed reactions involve bromohydrin salts as precursors to rearrangement products. These are sharp distinctions, and provide the cleanest examples of the two extreme mechanisms for epoxide-[Pg.760]

Effect of Epoxide Structure on Rate of Cure. The rate at which photosensitized epoxides are converted from the liquid to the solid state is influenced by the epoxide structure. Some photosensitized epoxides remain liquid even after prolonged exposure to the output of a mercury arc, while others solidify in less than one second. Rates at which various epoxides become tack-free are shown in Table VIII. 

FIGURE 10.10 Cleavage of a nonphenolic (3-0-4 structure and further reaction alternatives of the intermediately (epoxide) structure. (Gierer, J., Wood Sci Technol, 14, 241-266, 1980.)... 

The use of kinetic resolution as a strategy in asymmetric synthesis has been reviewed extensively [33,34]. The availability of epoxides in racemic form and the lack of effective enantioselective methods for preparing several important epoxide structural classes renders kinetic resolution by ARO a potentially powerful tool. For kinetic resolutions in which recovery of unreacted substrate is targeted, a cheap and easily handled reagent is desirable for effecting the resolution. Ideally, the ring-opened product would be of synthetic value, and each component of the kinetic resolution (unreacted substrate, product, and catalyst) would be easily isolated in pure form. 

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