114781-14-5Relevant articles and documents
Enzymatic- and iridium-catalyzed asymmetric synthesis of a benzothiazepinylphosphonate bile acid transporter inhibitor
Cowan, David J.,Collins, Jon L.,Mitchell, Mark B.,Ray, John A.,Sutton, Peter W.,Sarjeant, Amy A.,Boros, Eric E.
, p. 12726 - 12734 (2014/01/17)
A synthesis of the benzothiazepine phosphonic acid 3, employing both enzymatic and transition metal catalysis, is described. The quaternary chiral center of 3 was obtained by resolution of ethyl (2-ethyl)norleucinate (4) with porcine liver esterase (PLE) immobilized on Sepabeads. The resulting (R)-amino acid (5) was converted in two steps to aminosulfate 7, which was used for construction of the benzothiazepine ring. Benzophenone 15, prepared in four steps from trimethylhydroquinone 11, enabled sequential incorporation of phosphorus (Arbuzov chemistry) and sulfur (Pd(0)-catalyzed thiol coupling) leading to mercaptan intermediate 18. S-Alkylation of 18 with aminosulfate 7 followed by cyclodehydration afforded dihydrobenzothiazepine 20. Iridium-catalyzed asymmetric hydrogenation of 20 with the complex of [Ir(COD)2BArF] (26) and Taniaphos ligand P afforded the (3R,5R)-tetrahydrobenzothiazepine 30 following flash chromatography. Oxidation of 30 to sulfone 31 and phosphonate hydrolysis completed the synthesis of 3 in 12 steps and 13% overall yield.
The first fully planar C5-conformation of homooligopeptides prepared from a chiral α-ethylated α,α-disubstituted amino acid: (S)-butylethylglycine (=(2S)-2-amino-2-ethylhexanoic acid)
Imawaka, Naoto,Tanaka, Masakazu,Suemune, Hiroshi
, p. 2823 - 2835 (2007/10/03)
An optically active α-ethylated α,α-disubstituted amino acid, (S)-butylethylglycine (=(2S)-2-amino-2-ethylhexanoic acid; (S)-Beg; (S)-2), was prepared starting from butyl ethyl ketone (1) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)-Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C-terminus, and a trifluoroacetyl group was used for the N-terminus of the peptides. The structures of tri-and tetrapeptides 5 and 6 in the solid state were solved by X-ray crystallographic analysis, and were shown to have a bent planar C5-conformation (tripeptide) and a fully planar C5-conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and 1H-NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl3 solution was also a fully planar C5-conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α-ethylated α,α-disubstituted amino acid is a planar C5-conformation.
Chemo-Enzymic Synthesis of Optically Active α,α-Disubstituted α-Amino Acids
Liu, Weiguo,Ray, Paul,Benezra, Steven A.
, p. 553 - 560 (2007/10/02)
A series of α,α-disubstituted α-amino esters was chemically synthesized and then resolved through enantioselective hydrolysis catalysed by a new enzyme isolated from crude Humicola langinosa lipase.This enzyme only accepts free amino esters as substrates with neither lipase activity toward olive oil nor esterase activity toward o-nitrophenyl butyrate.It is unique in that it successfully catalyses the resolution of amino esters with two large α-alkyl groups including aliphatic, aromatic and cyclic amino esters.Examples of resolutions where the alkyl groups differ in size by as little as a single carbon atom have been demonstrated.For determination of absolute configuration, some of the optically active α,α-disubstituted amino acids were also prepared through Schoellkopf's asymmetric synthesis and the structures were verified by X-ray crystallography.A model depicting the substrate binding site of the enzyme is proposed.