10307-61-6Relevant articles and documents
Asymmetric hydrogenation routes to deoxypolyketide chirons
Zhou, Jianguang,Ogle, James W.,Fan, Yubo,Banphavichit, Yorawit,Zhu, Ye,Burgess, Kevin
, p. 7162 - 7170 (2007)
Asymmetric hydrogenations of monoenes and dienes were performed to obtain terminal deoxypolyketide fragments A and the corresponding internal Chirons B and C. The chiral N-heterocyclic carbene catalyst 1 was used throughout. Modest selectivities for hydrogenations of simple monoenes relayed into high selectivities for preparations of the terminal deoxypolyketide fragments in which either two hydrogenations or one and an optically pure starting material were used. Curiously, the face selectivities for hydrogenation of α,β-unsaturated esters were consistently opposite to those that had been observed for styrene and stilbene derivatives in previous work, and to closely related allylic alcohol and ether derivatives in this work. Plausible mechanisms for this differing behavior were deduced by using DFT calculations. It appears that the origin of the unusual stereoselectivity for the ester derivatives is transient metal-coordination of the ester carbonyl whereas there is no evidence that the allylic alcohol or ethers coordinate. The routes developed to α,ω-functionalized internal deoxypolyketide fragments are extremely practical. These begin with the Roche ester being converted into alkene and, in one case, diene derivatives. Catalyst control prevails in the hydrogenations of these substrates, but there is a significant "substrate vector" (a term we used to describe the influence of the substrate on a catalyst-controlled reaction). This is determined by minimization of 1,3-allylic strain and, in some cases, syn pentane interactions. This substrate vector can be constructively paired with the (dominant) catalyst vector by use of the appropriate enantiomer of 1. In the hydrogenation of a diene derivative, two chiral centers could be formed simultaneously with overall 11:1.0 selectivity; this is the first time this has been achieved in any asymmetric synthesis of a deoxypolyketide fragment. Throughout, diastereo-selectivities of the crude material in the syntheses of α,ω-functionalized internal deoxypolyketide fragments were in excess of 11:1.0 and chromatographically purified samples could be isolated in high yields with dr (dr = diastereomeric ratio) values consistently in excess of 40:1.0.
Total synthesis of (S)-(+)-ent-phomapyrones B and surugapyrone B
Ohmukai, Hiroaki,Sugiyama, Yasumasa,Hirota, Akira,Kirihata, Mitsunori,Tanimori, Shinji
, p. 1090 - 1100 (2020)
Phomapyrone B (1), the 2-pyrones isolated from the phytopathogenic fungus Leptosphaeria maculans, has been synthesized as the enantiomeric form starting from (S)-2-methylbutanol (4). Surugapyrone B (3) isolated from Streptmyces sp. USF-6280 as an antioxidant has also been synthesized as a natural form. The absolute configuration of phomapyrone B (1) was estimated to be the (R)-form and that of surugapyrone B (3) being the (S)-form. A series of 2-pyrone derivatives 17 have been synthesized through the established procedure and their DPPH radical-scavenging activities have also been evaluated.
Quantitation and Enantiomeric Ratios of Aroma Compounds Formed by an Ehrlich Degradation of l -Isoleucine in Fermented Foods
Matheis, Katrin,Granvogl, Michael,Schieberle, Peter
, p. 646 - 652 (2016)
The conversion of parent free amino acids into alcohols by an enzymatic deamination, decarboxylation, and reduction caused by microbial enzymes was first reported more than 100 years ago and is today known as the Ehrlich pathway. Because the chiral center at the carbon bearing the methyl group in l-isoleucine should not be prone to racemization during the reaction steps, the analysis of the enantiomeric distribution in 2-methylbutanal, 2-methylbutanol, and 2-methylbutanoic acid as well as in the compounds formed by secondary reactions, such as ethyl 2-methylbutanoate and 2-methylbutyl acetate, are an appropriate measure to follow the proposed degradation mechanism in the Ehrlich reaction. On the basis of a newly developed method for quantitation and chiral analysis, the enantiomers of the five metabolites were determined in a great number of fermented foods. Whereas 2-methylbutanol occurred as pure (S)-enantiomer in nearly all samples, a ratio of almost 1:1 of (S)- and (R)-2-methylbutanal was found. These data are not in agreement with the literature suggesting the formation of 2-methylbutanol by an enzymatic reduction of 2-methylbutanal. Also, the enantiomeric distribution in 2-methylbutanoic acid was closer to that in 2-methylbutanol than to that found in 2-methylbutanal, suggesting that also the acid is probably not formed by oxidation of the aldehyde as previously proposed. Additional model studies with (S)-2-methylbutanal did not show a racemization under the conditions of food production or during workup of the sample for volatile analysis. Therefore, the results establish that different mechanisms might be responsible for the formation of aldehydes and acids from the parent amino acids in the Ehrlich pathway.