Biological valorization of lignin-derived vanillin to vanillylamine by recombinant E. coli expressing ω-transaminase and alanine dehydrogenase in a petroleum ether-water system

Transaminase biocatalysis shows immense potential in industrial applications, and optimizations of both proteins and processes are of great importance. Transaminases (TAs) are one of the most promising biocatalysts in organic synthesis for the preparation of chiral amino compounds. The concise reaction, excellent enantioselectivity, environmental friendliness and compatibility with other enzymatic or chemical systems have brought TAs to the attention of scientists working in the area of biocatalysis. However, to utilize TAs in a more efficient and economical way, attempts have to be made to optimize their performance. The demand for various substrate specificities, stability under non-physiological conditions and higher conversions in reversible reactions have been targeted and investigated thoroughly. A number of both protein- and process-based strategies have been developed to improve TAs and systems involving TAs. Moreover, by combination with other enzymes in cascade reactions or even in more complex systems, so called synthetic biology and systems biocatalysis, TAs can be biocatalysts with immense potential in the industrial production of high-value chemical products. This review will highlight strategies for optimization of TAs and will discuss a number of elegant systems for improving their performance. Transaminase biocatalysis has been, and will continue to be, one of the most interesting topics in green organic synthesis.

Dwindling petroleum resources and increasing environmental concerns have stimulated the production of platform chemicals via biochemical processes through the use of renewable carbon sources. Various types of biomass wastes, which are biodegradable and vastly underutilized, are generated worldwide in huge quantities. They contain diverse chemical constituents, which may serve as starting points for the manufacture of a wide range of valuable bio-derived platform chemicals, intermediates, or end products via different conversion pathways. The valorization of inexpensive, abundantly available, and renewable biomass waste could provide significant benefits in response to increasing fossil fuel demands and manufacturing costs, as well as emerging environmental concerns. This review explores the potential for the use of available biomass waste to produce important chemicals, such as monosaccharides, oligosaccharides, biofuels, bioactive molecules, nanocellulose, and lignin, with a focus on commercially viable technologies.

An efficient process was developed to obtain furfurylamine with very high yield (∼92%) through the reductive amination of furfural under a mild reaction condition. A simple and highly efficient method was developed for the transformation of furfural (a biomass derived aldehyde) to furfurylamine by reductive amination using an aqueous solution of ammonia and molecular hydrogen as an amine source and a reducing agent, respectively. By choosing a suitable catalyst, such as Rh/Al 2 O 3 , and reaction conditions, a very high selectivity of furfurylamine (∼92%) can be achieved within the reaction time of 2 h at 80 °C. A detailed analysis of the reaction system sheds some light on the reaction pathway and provides an understanding about each elementary step. The reaction was believed to proceed via an imine pathway although no such intermediate was detected because of the highly reactive nature. Optimization of different reaction parameters such as hydrogen pressure, temperature and substrate/ammonia mole ratio is shown to be critical to achieve high selectivity of furfurylamine. Time-dependent reaction profiles suggested that a Schiff base type intermediate was in the detectable range, which offers indirect evidence of the formation of imine. Competitive hydrogenation and amination of an aldehyde group were strongly dictated by the nature of the metal used. The studied protocol represents an environmentally benign process for amine synthesis, which can be effectively extended to the other aldehydes also. The studied catalyst could be recycled successfully without any significant loss of catalytic activity.