The migration of energy production from environmentally hazardous methods to greener methods, exploring renewable sources, is one of the main goals of humanity for the XXI century. Nonetheless, our society is still largely dependent on fossil fuels for the majority of its key activities and will still be for the foreseeable future. This dependence urges the finding of ways to mitigate the environmental impact of the usage of fossil fuels, in particular oil. Sulphur compounds present in crude oil are one of the leading causes of the harmful environmental effects caused by its combustion. For this reason, increasingly lower concentrations of sulphur compounds are demanded, at the governmental level, on the refined oil. Unfortunately, the desulphurization of crude oil, which is currently achieved by chemical hydrodesulphurization, also presents harmful environmental effects. Thus, cleaner methods for desulphurizing crude oil are also needed. Currently, the most promising, with little environmental impact, desulphurization method is the biodesulphurization procedure called the ‘4S pathway’ carried out by three enzymes of the dszABC gene cluster encoded in the plasmid of the bacterium Rhodococcus erythropolis. In addition, a chromosome encoded flavin reductase (DszD) supplies FMNH₂ to the flavin-dependent enzymes of the pathway. Unfortunately, the 4S pathway is not currently attractive for industrial application, due mainly to the low kinetic efficiency of the enzymes that compose it. Therefore, we urgently need to find ways to enhance the 4S pathway, turning it into a viable complement to the current methods of desulphurization of crude oil. In this review, current methods of desulphurization of crude oil are discussed, and the state of the art of the 4S pathway is analyzed. We point out directions and strategies to improve the efficiency of biodesulphurization, to make it attractive and profitable at an industrial scale.

Plant‐derived natural compounds have been used for treating diseases since prehistorical times. The supply of many plant‐derived natural compounds for medicinal purposes, such as thebaine, morphine, and codeine, is primarily dependent on opium poppy crop harvesting. This dependency adds an extra risk factor to ensuring the supply chain because crops are highly susceptible to environmental conditions. Emerging technologies, such as biocatalysis, might help to solve this problem by diversifying the sources of supply of these compounds. Here we review the first committed step in the production of alkaloid painkillers, the production of S‐norcoclaurine, and the enzymes involved. The improvement of these enzymes can be carried out experimentally by directed evolution and rational design strategies, supported by computational methods, to create variants that produce the S‐norcoclaurine precursor for alkaloid painkillers in heterologous organisms, meeting the pharmaceutical industry standards and needs without depending on opium poppy crops.

(S)-Norcoclaurine is synthesized in vivo through a metabolic pathway that ends with (S)-norcoclaurine synthase (NCS). The former constitutes the scaffold for the biosynthesis of all benzylisoquinoline alkaloids (BIAs), including many drugs such as the opiates morphine and codeine and the semi-synthetic opioids oxycodone, hydrocodone, and hydromorphone. Unfortunately, the only source of complex BIAs is the opium poppy, leaving the drug supply dependent on poppy crops. Therefore, the bioproduction of (S)-norcoclaurine in heterologous hosts, such as bacteria or yeast, is an intense area of research nowadays. The efficiency of (S)-norcoclaurine biosynthesis is strongly dependent on the catalytic efficiency of NCS. Therefore, we identified vital NCS rate-enhancing mutations through the rational transition-state macrodipole stabilization method at the Quantum Mechanics/Molecular Mechanics (QM/MM) level. The results are a step forward for obtaining NCS variants able to biosynthesize (S)-norcoclaurine on a large scale.