55058-51-0Relevant articles and documents
Microbial reduction and in situ product crystallization coupled with biocatalyst cultivation during the synthesis of 6R-dihydrooxoisophorone
Buque-Taboada, Evelyn M.,Straathof, Adrie J. J.,Heijnen, Joseph J.,Van Der Wielen, Luuk A. M.
, p. 1147 - 1154 (2005)
An in situ product crystallization procedure was developed for a crystalline product formed during microbial reduction coupled with cell cultivation. The model reaction was the asymmetric reduction of 4-oxoisophorone (OIP) by baker's yeast (Saccharomyces cerevisiae). Yeast cells were cultivated fed-batch to reach a maximum concentration of 30 gdw·L-1. The desired product, 6R-dihydrooxoisophorone (DOIP), may be further reduced by baker's yeast to an unwanted by-product; thus, DOIP was removed immediately from the fermenter via an external crystallization loop in this procedure. The OIP reduction rate was five times higher (?0.33 mmol·gdw -1·h-1) as compared to the reduction rate with resting cells. OIP reduction was started when the optimum cell concentration had already been reached in the reactor because the substrate (OIP) at ≥55 mM concentration inhibited cell growth. An appropriate supply of glucose as carbon and energy source was necessary to support the coupled reactions involving cell growth and maintenance and product formation while avoiding formation of metabolic by-products. Final DOIP yield and selectivity were 85% and 99%, respectively, while over 100 g·L-1 of product was obtained in the crystallizer. The product crystals with favorable properties were readily recovered from the crystallizer. These results indicate that product crystallization is not impaired by the solutes present in the fermentation medium.
An engineered old yellow enzyme that enables efficient synthesis of (4R,6R)-actinol in a one-pot reduction system
Horita, Shoichiro,Kataoka, Michihiko,Kitamura, Nahoko,Nakagawa, Takuya,Miyakawa, Takuya,Ohtsuka, Jun,Nagata, Koji,Shimizu, Sakayu,Tanokura, Masaru
, p. 440 - 445 (2015/03/05)
(4R,6R)-Actinol can be stereo-selectively synthesized from ketoisophorone by a two-step conversion using a mixture of two enzymes: Candida macedoniensis old yellow enzyme (CmOYE) and Corynebacterium aquaticum (6R)-levodione reductase. However, (4S)-phorenol, an intermediate, accumulates because of the limited substrate range of CmOYE. To address this issue, we solved crystal structures of CmOYE in the presence and absence of a substrate analogue p-HBA, and introduced point mutations into the substrate-recognition loop. The most effective mutant (P295G) showed two- and 12-fold higher catalytic activities toward ketoisophorone and (4S)-phorenol, respectively, than the wild-type, and improved the yield of the two-step conversion from 67.2 to 90.1%. Our results demonstrate that the substrate range of an enzyme can be changed by introducing mutation(s) into a substrate-recognition loop. This method can be applied to the development of other favorable OYEs with different substrate preferences.
Reduction of aliphatic and aromatic cyclic ketones to sec-alcohols by aqueous titanium trichloride/ammonia system. Steric course and mechanistic implications
Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
, p. 2235 - 2243 (2007/10/03)
In contrast to the dissolved metal and metal hydride reductions, the reduction of cyclic ketones by the aqueous TiCl3/NH3 system favours the formation of the less thermodynamically stable axial alcohol. The ammonium ion formed in situ is essential for the reduction to proceed because it behaves as a mild Br?nsted acid in basic medium and favours the protonation of the intermediate ketyl. The corresponding α-hydroxy radical is then rapidly reduced under conditions where the first electron transfer to the substrate takes place. We suggest that the stereoselectivity is determined by the second reduction step, which occurs through the less hindered transition state, regardless of whether the radical to be reduced is thermodynamically favoured or not.
