Early Studies and Concepts of MCR Chemistry

Although organic chemistry as a science, including that of the MCRs, began many billions of years ago [24], the first MCR was accomplished in 1838 [7,25]. Progress in MCRs was rather slow for the next century, but in the past few years the combinatorial chemistry of the MCRs has become unusually active, and their libraries are currently a vital area of industrial chemical research [22], Following the identification of MCRs, it was soon realized that this was a particularly efficient method of searching for new products [3-5, 20-22], as chemical compounds formed by a suitable MCR were always synthesized more efficiently than by any other multistep procedure. 

When life on earth first began, many sequences of chemical reactions formed a vast variety of biochemical compounds as their libraries. Within the natural atmosphere many chemical compounds were formed, and even today the chemistry of nature proceeds not only by reactions of two components, but also by MCRs of three and more educts. In this way, many different chemical compounds are formed simultaneously as libraries. In his famous experiments, Miller showed how some a-amino acids and their derivatives were formed by the S-3CR (S = Strecker) [7,31]. 

It is assumed that adenine, an essential component of DNA and RNA, was formed from five units of hydrogen cyanide, and this process undoubtedly played a major role in the development of the first living cells [24]. 

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