Ring-Modified

FIGURE 27 14 A section of polystyrene showing one of the benzene rings modified by chloromethylation Indi vidual polystyrene chains in the resin used in solid phase peptide synthesis are con nected to one another at various points (cross linked) by adding a small amount of p divinylbenzene to the styrene monomer The chloromethylation step is carried out under conditions such that only about 10% of the benzene rings bear —CH2CI groups... 

Another representative highlight of the regioselective O-acylation work undertaken at QEC can be found in Richardson s selective O-pivaloylation of sucrose, which led to two papers with Les Hough and Manjit Chowdhary. One of these was on the regioselective O-pivaloylation itself, the other on the applications of the pivalate products in the preparation of various ring-modified sucrose derivatives. 

The (3-lactam antibiotics structurally resemble the terminal D-alanyl-D-alanine (o-Ala-o-Ala) in the pen-tapeptides on peptidoglycan (murein) (Fig. 45.1). Bacterial transpeptidases covalently bind the (3-lactam antibiotics at the enzyme active site, and the resultant acyl enzyme molecule is stable and inactive. The intact (3-lactam ring is required for antibiotic action. The (3-lactam ring modifies the active serine site on transpeptidases and blocks further enzyme function. 

Lactone Ring-Modified 4-Amino Etoposide Analogs... 

Complex 2 also proved valuable in attaching the ferrocene unit to chloromethylated polystyrene. Treatment of chloromethylated styrene (18% of the phenyl rings modified) with 2 under basic conditions afforded polymer 6. Polymer 7 was then prepared and found to have UV-Vis spectroscopic data analogous to monomer 4 and polymer 5. 

Chart 12 D-ring modified and D-secopaclitaxel derivatives investigated by Snyder and... 

For examples of ring-modified mitosene or mitomycin analogues, see K6hler,... 

Merckle, L. Dubois, J. Place, E. Thoret, S. Gueritte, R Guenard, D. Poupat, C. Ahand, A. Potier, P. Semisynthesis of D-ring modified taxoids novel thia derivatives of docetaxel. J. Org. Chem., 2001, 66 5058-5065. 

The introduction of bridging groups on the thiophene ring modifies the physical and chemical properties of the polymers obtained. The energy of the optical absorption is reduced in FEDOT, Fig. 9.2(k), and poly(ijothia-naphthalene), (PITN) (Wudl et al., 1984), so that in the conductive state thin films are transparent. PEDOT shows high electrochemical stability in the oxidised state and, when combined with poly(styrenesulphonic acid) counter ions, can be processed from aqueous solution. 

Structure of 3,3, 5,5 -tetraiodo-L-thyronine (T4). T4 is a substituted tyrosine or a diphenylether derivative of alanine. Positions in the outer phenolic ring have prime designations, in contrast to those in the inner ring. T4 is iodinated at positions 3 and 5 in both rings. [Modified and reproduced with permission from V. Cody, Thyroid hormone interactions molecular conformation, protein binding, and hormone action. Endocr. Rev. 1,140 (1980). (c)1980by the Endocrine Society.]... 

Sawada, S., Yaegashi, T., Furuta, T., Yokokura, T., Miyasaka, T. Chemical modification of an antitumor alkaloid, 20(S)-camptothecin E-lactone ring modified water-soluble derivatives of 7-ethylcamp-tothecin. Chem. Pharm. Bull. 1993, 41, 310-313. 

Fig. 2. Phenolic hydroxyl, B- and C-ring modified cannabinoid analogs...

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