Side Chain Chemistry

A few reactions of the taxol side chain are of interest. The taxoid cephalomannine (8.7.1) co-occurs with taxol, and there is thus a potential for increasing the supply of taxol by using cephalomannine as a substrate. A simple conversion of cephalomannine to taxol was achieved by benzoylation and ozonolysis to the ketoamide 8.7.2, followed by treatment with -phenylenediamine under acidic conditions. The o-phenylenediamine induces a cleavage of the ketoamide to the amine, and intramolecular O— N acyl transfer gives rise to taxol in good overall yield (336). 

Cephalomannine is not easily separated from taxol by chromatographic methods, but three chemical methods for accomplishing this 

Finally, selective N-debenzoylation of taxol has been achieved by reaction with di-t-butyl dicarbonate with 2 -(benzyloxycarbonyl)-7-(triethylsilyl)taxol to give the carbamate 8.7.3, followed by treatment with base and deprotection. Using this chemistry, taxol can be converted to docetaxel in 39% yield, and various N-acyl analogs of taxol can also be prepared through intermediate 8.7.4 (340). 

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Kim, S.J., Kang, S.H., Park, K.-M., Kim, H Zin, W.-C., Choi, M.-G. and Kim, K. (1998) Trinuclear Gold(l) Pyrazolate Complexes Exhibiting Hexagonal Columnar Mesophases with Only Three Side Chains. Chemistry of Materials, 10, 1889-1893. 

In cycloaddition reactions the [6,6] double bonds of Cjq exhibit a dienophilic character. A large variety of cycloadditions have carried out with Cjq and the complete characterization of the products, mainly monoadducts, has greatly increased our knowledge of fullerene chemistry. These chemical transformations also provide a powerful tool for the functionalization of the fullerene sphere. Almost any functional group can be covalently linked to Cjq by the cycloaddition of suitable addends. Some types of cycloadducts exhibit a remarkable stability for example, they can be thermally treated up to 400 °C without decomposition. This is an important requirement for further side-chain chemistry as well as for possible applications of the new fullerene derivatives, which may be of interest due to their biological activity or as new materials. 

Further side-chain chemistry can be carried out either at one of the side chains attached to the five-membered ring [228-232] or at the pyrrolidine nitrogen [215, 224, 231, 233-239], For example, upon heahng 3-triphenylmethyloxazolidin-5-one (210) at reflux for 16 h with Cjq in equimolar amounts, 211 can be isolated in 39% yield [204], Subsequent treatment of 211 with trifluoromethanesulfonic acid, then with pyridine and dansyl chloride (DnsCl) yields the dansyl pyrrolidine derivative 213 in 76% yield (Scheme 4.35). The amine 212 is an intermediate in this reachon. 

This synthetic approach offers many opportunities, both with molecular weight control and side-chain chemistry, for tailoring molecular structure to prepare different mesophases and optimize physical properties for nonlinear optical applications. 

The hydrogenation of 28, which is readily accessible from dehydrolinalol (27), was investigated as an alternative entry into the side chain chemistry. Ru(BlNAP)-or Ru(MeOBlPHEP)-catalyzed hydrogenation of this y-oxo-substituted olefin afforded 23 with only 64 and 77% ee, respectively. Remarkably, MeOBlPHEP diphosphines containing P(2-furyl)2 moieties afforded ee s >90%, the best ligand found so far being the unsymmetrical ligand (2-furyl)2-MeOBlPHEP [21]. 

COMT is widely distributed in the body and is primarily found on the outer plasma membrane of cells. Even red blood cells have the enzyme. As with PNMT, S-adenosylme-thionine is the source of the methyl group. The enzyme s specificity is toward the catechol nucleus the side chain chemistry seems irrelevant. It is only the meta-OH that is methylated. Magnesium is a requirement. 

A semiempirical/theoretical ionic model was derived to cor-relate and interrelate the ultrastructure morphology, surface charge, surface chemistry, and surface molecular motions of a model semicrystalline hydrophobic triblock copolymer to thrombogenesis. This chapter addresses the aspects of ultra-structure order vs. disorder, primary and secondary molecular motions, surface and side chain chemistry, thrombogenesis, and the resultant ionic model. This model can be extrapolated to predict the relative thrombogenic responses of various crystalline and semicrystalline hydrophobic polymeric substrates. 

We worked with the precept that morphologically ordered polymeric systems, of given side chain chemistry, can sequester ions, which can subsequently serve as an ionic array/tern plate for ordered protein adsorption, for example, epitaxial crystallization. Additionally, we addressed the effect of side chain motion of the substrate on the epitactic process based, in part, on... 

Some coenzymes participate in group-transfer reactions that are difficult to carry out with amino acid side chain chemistries alone. For example, none of the side chains of the normal 20 amino acids can accept an amino group easily. On the other hand, the coenzyme pyridoxal phosphate has a carbonyl group that is well adapted to accepting or donating amino groups. 

Statz AR, Barron AE, Messersmith PB. lYotein, cell, and bacterial fouling resistance of polypeptoid-modified stufaces Effect of side-chain chemistry. Soft Matter 2008 4 131-139. Statz AR, Meagher RJ, Barron AE, Messersmith PB. New pep-tidomimetic polymers for antifouling surfaces. J Am Chem Soc 2005 127 7972-7973. 

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