Heterocyclic combinatorial library products

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). 

The combinatorial decoration or derivatization of existing natural products is a popular method for library creation. Among targets for such exercises are the alkaloids yohimbine and scopolamine, terpenoids and steroids, and the heterocyclic peptide antibiotic GE-2270A (Figure 11). In the latter case, combinatorial variation was instrumental in the discovery of a developmental candidate now in clinical trials at Vicuron. Pfizer, the world s largest pharmaceutical company, recently acquired Vicuron for the sum of 1.9 billion, a mark of approval for natural product-based combinatorial chemistry. 

That green method can be applied to heterocyclic or aryl aldehydes in combination with phenylethyl, benzyl, and aliphatic amines. The authors used a variety of amines as a library of this combinatorial method. Propatgylamine gave a product that could be further elaborated via click-chemistiy approaches iV-Boc-ethylene-diamine gave a product whose exocyclic amine moiety could be further reacted to give potential DDX3 inhibitors (Scheme 9.17). 

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