Making drugs out of sunlight and thin air: An emerging synergy of synthetic biology and natural product chemistry

Nature has long served as a rich source of structurally diverse small organic molecules with medicinally relevant biological activities. Despite the historical success of these so-called natural products, the enthusiasm of big pharma to explore these compounds as leads in drug design has waxed and waned. A major contributor to this is their often inherent structural complexity. Such compounds are difficult (often impossible) to access synthetically, a hurdle that can stifle lead development and hinder sustainable large-scale production of promising leads for clinical evaluation. However, in recent years, an emerging synergy between synthetic biology and natural product chemistry offers the potential for a renaissance in our ability to access natural products for drug discovery and development. Advances in genome sequencing, bioinformatics and the maturing of heterologous expression platforms are increasing, enabling the study, and ultimately, the manipulation of plant biosynthetic pathways.The triterpenes are one of the most structurally diverse families of natural products and arguably one of the most underrepresented in the clinic. The plant kingdom is the richest source of triterpene diversity, with >20,000 triterpenes reported so far. Transient expression of genes for candidate enzymes and pathways in amenable plant species is emerging as a powerful and rapid means of investigating and harnessing the plant enzymes involved in generating this diversity. Such platforms also have the potential to serve as production systems in their own right, with the possibility of upscaling these discoveries into commercially useful products using the same overall basic procedure. Ultimately, the carbon source for generation of high-value compounds in plants is photosynthesis. Therefore, we could, with the help of plants, be producing new medicines out of sunlight and thin air in green factories in the not too distant future.