Polymer-supported derivative

Kim and Park et al. have reported a polymer-supported derivative (4), which, together with the enzyme, can be recycled and reused [27]. 

For application in an electrochemical enzyme membrane reactor, polymer-supported derivatives of 9 have been synthesized, which could be retained by ul-trafiltration membranes and were thus retained within the electroenzymatic reactor [31, 40]. 

Completion of the synthesis of hydroxy-1,4-benzodiazepines was achieved analogously as before acylation of 31 with Fmoc amino acid fluorides, removal of the Fmoc protecting group, cyclisation and alkylation afforded fully functionalised polymer-supported derivatives 34 that were cleaved from the resin by treatment with TFA/Me S/HjO (85 10 5) at r.t. to give products 35 in purities > 80% and in good overall yields. 

In the same context, another racemisation ruthenium catalyst, bearing a benzyloxy function, was synthesised by the same group and was successfully applied to similar reactions, providing the DKR of a wide range of functionalised alcohols in excellent yields and enantioselectivities (>99% ee). The corresponding polymer-supported derivative was also synthesised and tested as a recyclable catalyst for the aerobic DKR of alcohols (Scheme 4.13) its... 

During the following years, different ruthenium complexes derived from catalysts 7 and 8 were designed and employed in DKR processes, optimizing their activity and stability. Ruthenium catalysts 9 [53], 10 [54], and 11 [55] are air-stable complexes, which can be used in DKR processes under ambient conditions. Kanerva and coworkers have recently reported the ruthenium complex 12, which presents a more simple and cost-efficient preparation, although its scope is not as broad as the scope of catalyst 8. With the aim of obtaining a recyclable catalyst. Park described a polymer-supported derivative 13 (Figure 14.6) obtained from ruthenium catalyst 9 [53]. 

Polymer supported xanthene derivatives have been used in the solid phase synthesis of 1-aminophosphinic acids, RCH(NH2)PH(0)0H, <%TL1647> and of C-terminal peptide amides <96JOC6326>. Xanthene units also feature in crown ethers <96JCS(P2)2091>, calixarenes <96JOC5670> and in a flexible template for a P-sheet nucleator <96JOC7408>. 

Even in solution the relative rigidity of the polymer support can play a significant role in the reactivity of attached functional groups. Contrasting studies conducted with chloromethylated derivatives of poly(arylene ether sulfone) (Tg 175°C), phenoxy resin (Tg= 65°C) and polystyrene (Tg= 105°C) allow evaluation of chain rigidity effects. We have shown that the rates of quaternization of chloromethylated poly(arylene ether sulfones) and phenoxy resin deviate from the anticipated second order process at... 

Devaky and Rajasree have reported the production of a polymer-bound ethylenediamine-borane reagent (63) (Fig. 41) for use as a reducing agent for the reduction of aldehydes.87 The polymeric reagent was derived from a Merrifield resin and a 1,6-hexanediol diacrylate-cross-linked polystyrene resin (HDODA-PS). The borane reagent was incorporated in the polymer support by complexation with sodium borohydride. When this reducing agent was used in the competitive reduction of a 1 1 molar mixture of benzaldehyde and acetophenone, benzaldehyde was found to be selectively reduced to benzyl alcohol. 

Polymer-supported reagents and other solid sequestering agents may be used to generate an array of 1,2,3,4-tetrasubstituted pyrrole derivatives using the Barton-Zard reaction as a key pyrrole formation reaction. Pure pyrroles are obtained without any chromatographic purification... 

Figure 6 Immobilization of [Mn(salen)Cl] derivatives in a pendant fashion (P — polymer support).

The synthesis of the first polymer-supported chiral Mn-salen derivatives was reported independently by Sivaram171 and Minutolo.171-173 Different monomeric Jacobsen-type units, containing two polymerizable vinyl groups, were copolymerized with styrene and divinylbenzene to yield the corresponding cross-linked polymers as a monolithic compact block.174-176 The less mobile system (Figure 19) with no spacer between the aromatic ring and the polymer backbone is less enantioselective. 

The synthesis of both enantiomers of vasicinone has been carried out using almost entirely polymer-supported reagents. The route was based on functionalisation of deoxyvasicinone by a highly selective bromination then via enantioselective reduction of the derived ketone <06SL2609>. 

In a recent study, another method for microwave-assisted heterocycle synthesis leading to a small set of imidazole derivatives has been reported [54], These pharmaceutically important scaffolds were synthesized utilizing polymer-bound 3-N,N-(dimethylamino)isocyanoacrylate. This polymer support was easily prepared by treatment of [4-(bromomethyl)phenoxy]methyl polystyrene with a twofold excess of the appropriate isocyanoacrylate potassium salt in N,N-dimethylformamide (Scheme 7.37). The obtained intermediate was subsequently treated with N,N-di-methylformamide diethyl acetal (DMFDEA) in a mixture of tetrahydrofuran and ethanol to generate the desired polymer-bound substrate. 

The soluble polymer support was dissolved in dichloromethane and treated with 3 equivalents of chloroacetyl chloride for 10 min under microwave irradiation. The subsequent nucleophilic substitution utilizing 4 equivalents of various primary amines was carried out in N,N-dimethylformamide as solvent. The resulting PEG-bound amines were reacted with 3 equivalents of aryl or alkyl isothiocyanates in dichloromethane to furnish the polymer-bound urea derivatives after 5 min of micro-wave irradiation (Scheme 7.75). After each step, the intermediates were purified by simple precipitation with diethyl ether and filtration, so as to remove by-products and unreacted substrates. Finally, traceless release of the desired compounds by cyclative cleavage was achieved under mild basic conditions within 5 min of micro-wave irradiation. The 1,3-disubstituted hydantoins were obtained in varying yields but high purity. 

The conversion of isothiocyanates to isonitriles under microwave conditions has been studied by Ley and Taylor using a polymer-supported [l,3,2]oxaphospholidine [119]. The use of 3-methyl-2-phenyl-[l,3,2]oxaphospholidine in solution is less favored [120] due to the associated toxicity and instability of the phosphorus-derived reagent, as well as the need to isolate the products from a complex reaction mixture by vacuum distillation. This drawback has been resolved by attaching the active [l,3,2]oxaphospholidine to a polymer matrix. 

Table 16 Traceless polymer-supported synthesis of 4,5-disubstituted 3-amino-1,2,4-triazole derivatives (Scheme 5)...

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