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Most of reported synthesis approaches for poly(ester amide)s suffer from the difficulty in controlling the sequence of amino acid and ester units, and also some environmental disadvantages. Herein, we developed a facile approach for the lipase-catalyzed synthesis of chiral L-/D-Asp-based poly(ester amide)s with alternating aspartate and hydroxyhexanoic acid (HA) units. In the Novozym 435-catalyzed polycondensation starting from four monomers, namely N-(6-hydroxyhexanoyl) aspartate diesters with an L- or D-aspartate configuration, and methyl or benzyl ester groups at the α or β-carbonyl positions of Asp, we successfully obtained the corresponding alternating poly(HA-alt-L/D-β-aspartate)s with α-benzyl or α-methyl ester groups. The L-aspartate diester monomer was preferred to the D-aspartate diester monomer in the Novozym 435-catalyzed polycondensation, and it also showed high regioselectivity, mainly forming the β-linkage of the aspartate unit. Among the four poly(ester amide)s, poly(HA-alt-L-α-benzyl-β-aspartate) has the highest molar mass of up to 13 000 Da and 98% β-linkage. The thermal properties and the aggregate microstructures of these alternating poly(HA-alt-L/D-aspartate)s were also compared and some interesting differences were observed. Our results also showed that these enantiopure poly(HA-alt-L/D-aspartate)s did not form a stereocomplex.

A simple and environmentally friendly method to synthesize spiropyrazolo[3,4- b ]pyridines derivatives starting from isatin, cyclic-1,3-diketone and 3-methyl-5-aminopyrazole was developed. With the optimized conditions for enzymes, solvents, enzyme loading and reaction time in hand, 9 compounds were obtained in acceptable yields. Moreover, the investigation in fluorescent properties of these products showed their potential application in the field of new fluorescent material.

Enzymes have been widely used as efficient, eco-friendly, and biodegradable catalysts in organic chemistry due to their mild reaction conditions and high selectivity and efficiency. In recent years, the catalytic promiscuity of many enzymes in unnatural reactions has been revealed and studied by chemists and biochemists, which has expanded the application potential of enzymes. To enhance the selectivity and activity of enzymes in their natural or promiscuous reactions, many methods have been recommended, such as protein engineering, process engineering, and media engineering. Among them, the additive approach is very attractive because of its simplicity to use and high efficiency. In this paper, we will review the recent developments about the applications of additives to improve the catalytic performances of enzymes in their natural and promiscuous reactions. These additives include water, organic bases, water mimics, cosolvents, crown ethers, salts, surfactants, and some particular molecular additives.