Aphanizomenon spp. have formed harmful cyanobacterial blooms in the Nakdong River during spring, autumn, and now in winter, and the expansion of blooming period and area, associated with the global warming is predicted. The genus Aphanizomenon has been described to produce harmful secondary metabolites such as off-flavors and cyanotoxins. Therefore, the production of harmful secondary metabolites from the Aphanizomenon blooms in the Nakdong River needs to be monitored to minimize the risk to both water quality and public health. Here, we sampled the cyanobacterial blooms in the Nakdong River and isolated ten Aphanizomenon strains, morphologically classified as Aphanizomenon flos-aquae Ralfs ex Bornet et Flahault 1888. Phylogenetic analysis using 16S rRNA and internal transcribed spacer (ITS) region nucleotide sequences confirmed this classification. We further verified the harmful secondary metabolites-producing potential of A. flos-aquae isolates and water samples containing cyanobacterial blooms using PCR with specific primer sets for genes involved in biosynthesis of off-flavor metabolites (geosmin) and toxins (microcystins, saxitoxins and cylindrospermopsins). It was confirmed that these metabolite biosynthesis genes were not identified in all isolates and water samples containing only Aphanizomenon spp. Thus, it is likely that there is a low potential for the production of off-flavor metabolites and cyanotoxins in Aphanizomenon blooms in the Nakdong River.
Significance: A recyclable polystyrene-supported ruthenium catalyst promoting racemization of secalcohols was developed and combined with a lipase to convert racemic sec-alcohols into the corresponding optically pure acetates via dynamic kinetic resolution (DKR). Thus, the DKR of racemic 1-phenylethanol with isopropenyl acetate (1.5 mol equiv) was performed at 25°C with catalyst 1, K 3 PO 4 (1.0 mol equiv) and Novozym 435 in toluene under aerobic conditions to give (R)-1-phenylethylacetate in 99% yield with 99% ee (for more results see scheme). Eight examples of the DKR of various secondary alcohols were demonstrated to afford the corresponding acetates in 86-99% yield with 92-99% enantiomeric purity.Comment: The combination of the enzymatic kinetic resolution with a metal-catalyzed racemization via hydrogen transfer was introduced for preparing enantiomerically pure alcohols by Williams in 1996 and Bäckvall in 1997. The authors previously reported on the racemization catalyst [2,3,4,5-Ph 4 ( 5 -C 4 CNH-i-Pr)]Ru(CO) 2 Cl for the dynamic kinetic resolution of a wide scope of secondary alcohols with lipases under argon (81-99% ee; ). In the current paper, they have developed an air-stable and recyclable racemization catalyst that was applicable to alcohol DKR at room temperature.
RuPh Ph Ph Ph OC CO Cl Ph OH Ph OH 1 K 3 PO 4 O O O 1 OAc Novozym 435 25 °C, 20 h toluene, air Ph OAc 1st: 99% (99% ee) 2nd: 99% (99% ee) 3rd: 95% (99% ee) 4th: 36% (99% ee) SYNFACTS Contributors:
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