Heterocycle library synthesis combinatorial libraries

The resin-bound polyamine was used as a template for the solid-phase synthesis of a range of heterocyclic compounds, such as cyclic ureas 25 and cyclic thioureas 26. This work exemplifies our ongoing efforts on the solid-phase assembly of individual acyclic and heterocyclic compounds and combinatorial libraries using short peptides as starting materials. 

At first, combinatorial chemistry focused on peptide and nucleotide libraries synthesis, but because poor pharmacokinetical properties cause poor oral availability of this kind of molecule, there is increasing interest in the development of new methods to prepare small, drug-tike molecules which obey lipinski s mle of five [303]. Heterocyclic compounds can offer a high degree of structural diversity and have proven to be useful as therapeutic agents. For these, there are recent advances in the preparation of heterocycles on solid supports [304]. The examples reported in this section are organized by their ring size. 

Keywords Absolute configuration, Amines, Amino acids, Carbenes, Cascade reactions, 2-chloro-2-cyclopropylideneacetates. Combinatorial libraries. Cycloadditions, Cyclobutenes, Cyclopropanes, Diels-Alder reactions. Heterocycles, Michael additions. Nitrones, Nucleophilic substitutions, Peptidomimetics, Palladium catalysis. Polycycles, Solid phase synthesis, Spiro compounds. Thiols... 

Fig. 12. Parallel synthesis of combinatorial libraries of heterocycles via resin-bound...

Combinatorial synthesis and screening of heterocyclic, drug-like scaffold libraries... 

Several unique heterocyclic fused-1,2,4-triazole structures have been published. Pyridine amination of 216 with O-mesitylenesulfonylhydroxylamine followed by condensation with various aryl and heterocyclic aldehydes and subsequent cyclization and oxidation gave triazolopyridines 217 <03TL1675>. Triazolopyridines 217 were utilized in the direct conversion to the triazolopyridine amides 218 with methylaluminoxane premixed with amines in a combinatorial library synthesis. A convenient synthesis of novel 4-(l,2,4-triazol-l-yl)-2-pyrazolines and their derivatives has been reported <03SC1449>. A novel triheterocyclic ring system, thieno[2,3-y][l,2,4]triazolo[l,5-a]azepines, has been published <03S1231>. 

Substituted heterocyclic compounds offer a high degree of structural diversity and have proven to be broadly and economically useful as therapeutic agents. The development of strategies for the synthesis of heterocyclic compounds on the solid phase is expanding as a greater understanding of how to carry out such reactions successfully is attained. We have reviewed the current status of heterocyclic combinatorially libraries [20]. 

A variety of heterocyclic compounds have been derived from the condensation of aldehydes with a-amino acids. Imines 1 (Fig. 3) are often used as intermediates in organic synthesis and are the starting point for chemical reactions such as cycloadditions, condensation reactions, and nucleophilic additions. The formation of imines via condensation of amines with aldehydes was first adopted for the reductive alkylation of resin-bound amino acids [29-31]. Imines have now been used as synthetic intermediates in the generation of a range of heterocyclic combinatorial libraries. 

This reaction was first reported by Hofmann in 1868. It is the synthesis of isonitriles (also known as isocyanides) from primary amines and chloroform in the presence of alkali and is known as the Hofmann isonitrile synthesis, Hofmann carbylamine reaction, or Hofmann carbylamine synthesis. This reaction has been used to test the presence of primary amines from the order of isocyanides. Alternatively, the isonitriles can be prepared by means of the treatment of formamide of primary amines with toluenesulfonyl chloride" or phosphorus oxychloride (POCls)." Currently, the isonitriles have gained much attention in organic synthesis because of their application as versatile building blocks for heterocycles and in multicomponent reactions to generate combinatorial libraries, such as that in the Passerini reaction and Ugi reaction ... 

Since the introduction of solid-phase peptide synthesis by Merrifield (1) nearly forty years ago, solid-phase techniques have been applied to the construction of a variety of biopolymers and extended into the field of small molecule synthesis. The last decade has seen the emergenee of solid-phase synthesis as the leading technique in the development and production of combinatorial libraries of diverse compounds of varying sizes and properties. Combinatorial libraries can be classified as biopolymer based (e.g., peptides, peptidomimetics, polyureas, and others [2,3]) or small moleeule based (e.g., heterocycles [4], natural product derivatives [5], and inorganie eomplexes [6,7]). Libraries synthesized by solid-phase techniques mainly use polystyrene-divinylbenzene (PS) derived solid supports. Owing to physieal and ehemical limitations of PS-derived resins, other resins have been developed (8,9). Most of these resins are prepared from PS by functionalizing the resin beads with oligomers to improve solvent compatibility and physical stability (8,9). 

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