Polymer-supported strategy

S Parallel Synthesis Using Soluble Polymer-Supported Strategies... 

Polymer-supported strategies of oligosaccharide syntheses are ideally suited to preparations of combinatorial oligosaccharide libraries since purification of all products of a particular synthetic step is done at the same time and it would not be expected that individual library members would be lost during the purification process. Both one-phase and two-phase polymer supported strategies have been examined, and a review was published recently [80]. More recent articles that were not discussed in this review include syntheses of disaccharide [81] and trisaccharide [82] libraries leading to the discovery of novel antibacterial agents [83], and prepa-... 

The N-to-C assembly of the peptide chain is unfavorable for the chemical synthesis of peptides on solid supports. This strategy can be dismissed already for the single reason that repeated activation of the carboxyl ends on the growing peptide chain would lead to a much higher percentage of racemization. Several other more practical disadvantages also tend to disfavor this approach, and acid activation on the polymer support is usually only used in one-step fragment condensations (p. 241). 

A strategy involving sequential 1,3-dipolar cycloadditions has been reported for the synthesis of novel bis-isoxazolo substituted piperidines 192a and 192b (Eqs. 18 and 19) [53]. It consists of the Michael addition of an unsaturated alkox-ide 185 to )3-nitrostyrene 184 followed by an INOC or ISOC reaction to provide isoxazolines 187-189 (Eq. 18 and Table 18). A polymer supported acyl chloride... 

Scheme 7.12 Reaction strategies for the polymer-supported synthesis of dialkylaminopropenones.

From a commercial viewpoint potential benefits can accrue from operating the methanol carbonylation process at low water concentration, provided that catalyst stability can be maintained. Strategies to achieve this include (i) addition of iodide salts to stabilise the Rh catalyst, (ii) heterogenisation of the Rh catalyst on a polymer support to restrict the catalyst to the reactor and (iii) replacement of Rh by a more robust Ir catalyst. These strategies, along with others for improving catalyst activity, will be discussed in the following sections. 

The preparation of polymer-supported iridium catalysts (61) and (62) for the stereoselective isomerization of double bonds using polystyrene based immobilized triphenyl phosphine were recently reported by Ley and coworkers (Fig. 4.5). The immobilized catalyst is potentially useful for deprotection strategies of aUyl ethers [130]. 

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