Abstract
A crude extract of earthworms was used as an eco-friendly, environmentally benign, and easily accessible biocatalyst for various organic synthesis including the asymmetric direct aldol and Mannich reactions, Henry and Biginelli reactions, direct three-component aza-Diels-Alder reactions for the synthesis of isoquinuclidines, and domino reactions for the synthesis of coumarins. Most of these reactions have never before seen in nature, and moderate to good enantioselectivities in aldol and Mannich reactions were obtained with this earthworm catalyst. The products can be obtained in preparatively useful yields, and the procedure does not require any additional cofactors or special equipment. This work provides an example of a practical way to use sustainable catalysts from nature.
Highlights
The exploitation of new catalysts in an environmentally benign manner has become crucially important in recent years [1]
In the absence of the crude earthworm extract, only a trace amount of product was observed in the model aldol reaction of 4cyanobenzaldehyde and cyclohexanone even after 120 h (Table 1, entry 10), indicating that the crude earthworm extract catalysed the aldol reaction in asymmetric manner
Nature is a vital source of catalysts, but the use of natural catalysts in organic synthesis is very limited, mainly due to the difficulties in isolation and purification of enzymes
Summary
The exploitation of new catalysts in an environmentally benign manner has become crucially important in recent years [1]. An earthworm, Lumbricus rubellus, produces alkaline serine proteases that show higher activity and stability than trypsins These enzymes are stable at temperature below 60uC over a wide range of pH 2–11, and are strongly resistant to organic solvents and detergents. They retain full activity for long years at room temperature. Nakajima et al reported that one of the earthworm serine protease acts on the hydrolysis of triacylglycerols [15] They reported the stereoselective reduction of carbonyl compounds using the cell-free extract from earthworms (Lumbricus rubellus) in the presence of NADH or NADPH as a coenzyme [16]. The earthworm species we used is Eisenia foetida (Annelida, Oligochaeta), known as red worm
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