goal in the field of asymmetric catalysis. Herein we report the synthesis and application of a new chiral 1,4bisphosphine, (2R,2′R)-bis(diphenylphosphino)-(1R,1′R)-dicyclopentane (1) (abbreviated (R,R)-BICP) (Figure 1) in the rhodium-catalyzed asymmetrichydrogenation of R-(acylamino)acrylic acids. The key feature of this ligand is that it contains two cyclopentane rings in its backbone which are present
Efficient Asymmetric Hydrogenations of (<i>Z</i>)-2-Acetamidoacrylic Acid Derivatives with the Cationic Rhodium Complex of (2<i>S</i>,4<i>S</i>)-MOD-BPPM
作者:Hisashi Takahashi、Kazuo Achiwa
DOI:10.1246/cl.1989.305
日期:1989.2
5′-dimethylphenyl)]phosphino]-2-[[[bis(4′-methoxy-3′,5′-dimethylphenyl)]phosphino]methyl]pyrrolidine) and its application to highly effective asymmetric hydrogenations of (Z)-2-acetamidoacrylic acid derivatives are described.
Mikrobiologisch hergestellte N-Acetyl-2,3-didehydroleucin-Acylase, Verfahren zu ihrer Gewinnung und ihre Verwendung
申请人:Degussa Aktiengesellschaft
公开号:EP0381997A1
公开(公告)日:1990-08-16
Gegenstand der Erfindung ist eine mikrobiologisch hergestellte N-Acetyl-2,3-didehydroaminosäure-Acylase und ein Verfahren zu ihrer Gewinnung aus Zoogloea ramigera DSM 4306. Das neue Enzym kann in einem gekoppelten Enzymsystem mit einer L-Leucindehydrogenase zur enzymatischen Umwandlung von N-Acetyl-2,3-didehydroleucin zu L-Leucin über die Zwischenstufen 2-Imino-4-methyl-pentansäure bzw. 2-Keto-4-methyl-pentansäure verwendet werden. Weiterhin kann die Acylase zur Herstellung von D- oder L-Tryptophylglycin aus D- oder L-Tryptophanamid und Glycin sowie von anderen Tryptophyldipeptiden aus Tryptophanamid und einer freien Aminosäure als Aminokomponente eingesetzt werden.
Carbohydrate Phosphinites as Practical Ligands in Asymmetric Catalysis: Electronic Effects and Dependence of Backbone Chirality in Rh-Catalyzed Asymmetric Hydrogenations. Synthesis of <i>R</i>- or <i>S</i>-Amino Acids Using Natural Sugars as Ligand Precursors
作者:T. V. RajanBabu、Timothy A. Ayers、Gary A. Halliday、Kimberly K. You、Joseph C. Calabrese
DOI:10.1021/jo970884d
日期:1997.8.1
Vicinal diarylphosphinites derived from carbohydrates are excellent ligands for the Rh(I)-catalyzed enantioselective asymmetric hydrogenation of dehydroamino acid derivatives, producing the highest enantioselectivity of any ligands directly prepared from natural products. The enantioselectivity can be enhanced by the appropriate choice of substituents on the aromatic rings of the phosphinites. For example, the use of phosphinites with electron-donating bis(3,5-dimethylphenyl) groups on phosphorus provides ee's up to 99% for a wide range of amino acids including some with easily removable N-protecting groups. Electron-withdrawing aryl substituents, on the other hand, decrease the enantioselectivity. Sense of chiral induction in the amino acid product depends on the relative juxtaposition of the vicinal diphosphinites on a given sugar backbone. When readily available D-glucopyranosides are used as the starting sugars, 2,3-phosphinites give the S-amino acids and 3,4-phosphinites give the R-amino acids. In the case of aromatic and heteroaromatic amino acids, enantioselectivities > 95% are consistently obtained. Practical considerations such as the ease of ligand synthesis, rates of reactions, catalyst turnover, and scope and limitations in terms of substrates are discussed. A possible explanation for the enhancement of enantioselectivity by electron-rich phosphinites is offered.