Synthesis s. a. C-Chain

Synthesis (s. a. C-Chain extension. Condensation, Friedel-Crafts ketone synthesis, Oxalic ester -)... 

Although many examples have been reported, the synthetic strategies followed for the preparation of side-chain polymers can be summarized as two different approaches (Figure 1.9) (a) direct introduction of fullerene itself or a Ciso-derivative into a preformed polymer and (b) synthesis of a C,so derivative that can be, in turn, directly homopolymerized or copolymerized together with other monomer(s). 

Structural drawings of carbohydrates of this type are called Haworth formulas, after the British chemist Sir Walter Norman Haworth (St Andrew s University and the University of Birmingham) Early m his career Haworth contributed to the discovery that carbohydrates exist as cyclic hemiacetals rather than m open chain forms Later he col laborated on an efficient synthesis of vitamin C from carbohydrate precursors This was the first chemical synthesis of a vitamin and provided an inexpensive route to its prepa ration on a commercial scale Haworth was a corecipient of the Nobel Prize for chem istry m 1937... 

The successfiil synthesis of a transparent soHd polymer electrolyte (SPE) based on PEO and alkoxysilanes has been reported (41). The material possessed good mechanical properties and high electrical conductivity (around 1.8 x 10 S/cm at 25°C) dependent on the organic—inorganic ratio and PEO chain length. 

Gou, D.M., Liu, Y.C., Chen, C.S. (1993) A Practical Chemoenzymatic Synthesis ofthe Taxol C-13 Side Chain N-Benzoyl-(2R,3S)-3-phenylisoserine. Journal of Organic Chemistry, 58, 1287-1289. 

Table II shows Tgs obtained from DSC traces. (Footnotes a and b in Table II show T s values of three reference polymers two PIBs, whose Mns are similar to the Mns of MA-PIB-MA used in the network synthesis, and a PDMAAm the difference in the Tg for the Mn=4,000 and 9,300 PIBs is due to the dependence of Tg on Mn(72)). The DSC traces of the networks exhibited two Tgs, one in the range of -63 to -52 °C (PIB domains) and another in the range of 90 to 115 °C (PDMAAm domains) indicating microphase separated structures. The Tgs associated with the PIB phase in the PDMAAm-1-PIB networks were higher than those of the reference homoPIBs which may be due to PIB chain-ends embedded in the glassy PDMAAm phase restricting segmental mobility. The Tg of the PIB phase in the PDMAAm-1-PIB increases by increasing the PIB content which may be due to an increase in crosslink density. In contrast, the Tg for the PDMAAm phase in the network decreases upon increasing the PIB content. Interaction of the (-CH2-CH-) moiety of the PDMAAm with the flexible PIB and thus the formation of a more flexible structure may explain this phenomenon.

A total synthesis of functionalized 8,14-seco steroids with five- and six-membered D rings has been developed (467). The synthesis is based on the transformation of (S)-carvone into a steroidal AB ring moiety with a side chain at C(9), which allows the creation of a nitrile oxide at this position. The nitrile oxides are coupled with cyclic enones or enol derivatives of 1,3-diketones, and reductive cleavage of the obtained cycloadducts give the desired products. The formation of a twelve-membered ring compound has been reported in the cycloaddition of one of the nitrile oxides with cyclopentenone and as the result of an intramolecular ene reaction, followed by retro-aldol reaction. 

P Rovero, S Pegoraro, F Bonelli, A Triolo. Side reactions in peptide synthesis dehydration of C-terminal aspartylamide peptides during side chain to side chain cyclization. Tetrahedron Lett 34, 2199, 1993. 

Similarly, iterative NRPSs operate in a linear fashion but utilize at least one domain or module multiple times for the synthesis of a single NRP product. Thus, peptides assembled by iterative synthetases contain short, repeating units of peptide building blocks. In such systems, the terminal PCP-TE (or infrequendy PCP-C) didomain is responsible for both condensation of the repeating peptide units and chain release from the assembly line. NRPs biosynthesized in this manner include enniatin, enterobactin, bacillibactin, " gramicidin and the depsi-peptides valinomycin and cereulide. Of these examples, condensation of the precursor peptides for both enterobactin and gramicidin S has been extensively studied and will be discussed in detail. 

M. Nomura, S. Shuto, M. Tanaka, T. Sasaki, S. Mori, S. Shigeta, and A. Matsuda, Nucleosides and Nucleotides. 185. Synthesis and biological activities of 4 -a-C-branched-chain sugar pyrimidine nucleosides, J. Med. Chem., 42 (1999) 2901-2908. 

---