Serine ionic properties

Moreover, Teo s group worked on the development and application of siloxy serine organocatalysts [30]. Particularly, when (S)-37 was used, the reaction could be performed in water with a consequent low environmental impact (Scheme 2.10a), and the onli-Mannich products 38 were isolated in interesting ee (np to 90%). Pursuing this research, in 2011, the same group has highlighted the remarkable properties of ionic liquids 39 as solvents (Scheme 2.10b, up to 99% ee) [31]. The developed strategy ensured the recyclability of the catalyst (S)-37 in Mannich reaction after three cycles, they obtained an identical stereoselectivity and reactivity as well as the ionic liquid preserved its biphasic properties, whereas the next three cycles displayed a decrease in ee and yield. 

The serine protease from Thermus caldophilus strain GK-24 [292] gave maximum activity at 90 °C in 20 min assays and had a broad pH optimum with casein as substrate. The enzyme showed hydrolytic activity on some small peptide substrates (e.g. CBZ-L-leu-L-tyr-NHj) and also possessed esterase activity. Hydrolysis of synthetic chromogenic peptides and esters is also a property of the recently described serine protease, caldolase, from Thermus strain ToK3 [293]. This enzyme contained 10% carbohydrate and four disulphide bonds, but neither calcium nor zinc were detected in the purified enzyme. Thermostability of the enzyme was high in 0.4 M NaCl, but in low ionic strength buffer rapid thermal denaturation occurred at 75 °C. Work has also been undertaken in this laboratory... 

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