The first organic molecule to be synthesized in a laboratory was urea by Friedrich Wöhler in 1828. Since then, techniques of organic synthesis have developed and advanced, with multi-step synthesis using retrosynthesis being revolutionary for the field of chemical research. The retrosynthetic framework for synthesis of organic molecules is designed to be efficient, economical and environmentally-friendly and is therefore an invaluable asset which has transformed approaches to organic chemical synthesis.
Retrosynthesis in Achieving Synthesis of Complex Target Molecules
Retrosynthesis is a method of chemical synthesis which involves “deconstructing” a target molecule into its readily available, simple starting materials in order to assess the best synthetic route. This is achieved by breaking the bonds of the target molecular structure into constituent fragments, known as synthons, and by conversion of functional groups into others, known as functional group interconversions.
The concept of retrosynthesis was framed and formalized by Elias James Corey, for which he won the Nobel Prize for Chemistry in 1990. Prior to this method becoming the standard practice, there was no formalized approach to organic chemical synthesis, and many methods involved significant trial and error with available simple molecules. By beginning with the target molecule, retrosynthesis allows chemists to work “in reverse”, by breaking up the complex target structure to arrive at the simple precursors. Often, there will be more than one possible synthetic route and retrosynthesis helps in discovering these routes and comparing them in terms of the cost, simplicity and feasibility of using different reagents and intermediates. In doing so, the most favorable, efficient route can be chosen before synthesis is started on an industrial scale.
Significance of Organic Synthesis of Natural Compounds
There are a vast number of biological materials existing in nature which are known to have powerful medicinal properties and are capable of being used for medical purposes to treat, suppress and even cure diseases. These naturally occurring complex molecules (secondary metabolites) may be extracts of plants or animal species and organic synthesis of these molecules is therefore an important area for chemical research. Retrosynthesis, by its molecule deconstruction approach, helps in understanding the complex nature of these natural products and provides multiple possibilities of synthetic routes, from which the most cost-effective and environmentally friendly path can be selected. This technique is especially useful for planning the synthesis of organic compounds, which have vastly more complex structures than inorganic compounds.
Retrosynthesis of Organic Molecules
Among the medications currently available for treating cancer, several of these are considered natural products. Paclitaxel, is a chemotherapy medication used to treat several types of cancer including breast, cervical, lung and pancreatic cancer and Kaposi’s sarcoma.
Preparation of Paclitaxel requires cutting several trees of Taxus brevifolia, a rare species of Pacific yew, and extracting the drug from the bark. In the early days of drug development, the bark was obtained from the tree by peeling, which destroyed the trees and meant that the supply of the drug was limited as well as the process being slow, now-renewable and non-environmentally friendly. At least one kilogram of bark was required to produce just 10g of the drug.
To reduce the impact on the environment, synthetic organic chemists played a vital role in synthesizing Paclitaxel in the laboratory using the retrosynthetic approach. In 1994, the first total synthesis of Paclitaxel was published by Robert A. Holton and his group at Florida State University, known as the Holton Taxol total synthesis. This is a multi-step retrosynthetic approach, which determined ‘Patchoulene oxide’ as the starting material. Today, there are many other well-known routes available to synthesize Paclitaxel, most of which are derived using retrosynthesis. Many natural product-based drugs in the market are also being synthesized utilizing retrosynthesis, which minimizes the costs for the projects and allows natural resources to be conserved.
Retrosynthesis provides the ability to choose the most feasible route for synthesis of an end product and the IQVIA Chemical Intelligence Synthesis Pathways module showcases the different paths (retrosynthetic/non-retrosynthetic) available.
The importance of chemical synthesis for organic compounds is evident and particularly the use of retrosynthesis for discovering new and improved synthetic routes. IQVIA Chemical Intelligence has 83,000+ paths registered in its Synthesis Pathways module. This includes multiple synthesis paths for important active pharmaceutical ingredients in the market, many of which are natural products, including complex total synthesis. Using IQVIA Chemical Intelligence data, alternate, cost-effective methods for the synthesis of complicated molecules can be found. The Synthesis Pathways module is a valuable source of information for synthesizing end products and is a highly effective tool to help identify potential users of intermediates.
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