Strychnos 1990 - 2004 - Crops for the Future

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Author Title Year Source title Reference Shibasaki, M., T. Iida and Y. M. A. Yamada Development of multifunctional asymmetric catalysts and their application to prac 1998 Journal of Synthetic Organic Chemistry Japan 56(5): 344-356 Abstract This article focuses on a new concept in catalytic asymmetric synthesis, which was first realized by the use of heterobimetallic complexes. As such complexes function at the same time as both a Lewis acid and a Bronsted base, similar to enzymes, they make possible a variety of efficient catalytic asymmetric reactions. This "heterobimetallic" concept has proven to be applicable to a variety of new asymmetric catalyses. We have already succeeded in asymmetric nitroaldol reactions catalyzed by the LaLi(3)tris (binaphthoxide) complex (LLB) and asymmetric Michael reactions catalyzed by the LaNa(3)tris (binaphthoxide) complex (LSB). Now the LLB catalyst could also be applied efficiently to the tandem inter-intramolecular asymmetric nitroaldol reaction, affording a synthetically useful bicyclic product with four newly generated chiral carbons in one pot. Furthermore we succeeded in the first direct asymmetric aldol reactions of aldehydes with unmodified ketones (up to 94% ee) by using a catalytic amount of LLB. While LLB was also effective in the hydrophosphonylation of aldehydes, asymmetric hydrophosphonylations of imines were efficiently catalyzed by the LnK(3)tris (binaphthoxide) complex (LnPB:Ln=rare earth metal such as La, Yb) (up to 96% ee). On the other hand, alkali metal free lanthanum complexes prepared from Ln(O-i-Pr)(3) (Ln=La or Yb) and 1,1'-binaphthol (BINOL) or 3-hydroxymethyl-BINOL were excellent catalysts for the asymmetric epoxidation of alpha,beta-unsaturated ketones (up to 94% eel. We also developed another type of heterobimetallic catalysts featuring group 13 elements such as Al or Ga as a central metal. Among them, the AlLibis(binaphthoxide) complex (ALB) is an effective catalyst for asymmetric Michael reactions of malonates or Horner-Wadsworth-Emmons reagents (up to 99% ee) and for asymmetric tandem Michael-aldol reactions. Applications bi this catalyst to syntheses of biologically important compounds such as 11-deoxy-PGF(1 alpha) and tubifolidine are also described. Furthermore the GaLibis (binaphthoxide) complex (GaLB) in combination with molecular sieves 4 A was found to be an efficient catalyst for asymmetric ring openings of a variety o f e p o x i d e s w i t h t - B u S H ( u p t o 9 7 % e e ) . Author Title Year Source title Reference Abstract Shimizu, S., K. Ohori, T. Arai, H. Sasai and M. Shibasaki Catalytic asymmetric synthesis of tubifolidine 1998 Journal of Organic Chemistry 63(21): 7547-7551 -
Author Title Year Source title Reference Shin K; Moriya M; Ogasawara K Enantio- and diastereocontrolled synthesis of (-)-19(s)-acetoxy-n-1-acetyl-20-epit 1998 Tetrahedron Letters 39(22): 3765-3768 Abstract An enantiocontrolled route to the 19-oxygenated pentacyclic Strychnos alkaloids has been demonstrated by the stereoselective synthesis of (-)-19(S)-acetoxy-N-1-acetyl-20-epitubifolidine. (C) 1998 Elsevier Science Ltd. All rights reserved. Author Title Year Source title Reference Abstract Visen, P. K. S., B. Saraswat, K. Raj, A. P. Bhaduri and M. P. Dubey Prevention of galactosamine-induced hepatic damage by the natural product logan 1998 Phytotherapy Research 12(6): 405-408 - Author Title Year Source title Reference Abstract Zhang, Z. and et al. Determination of strychnine and brucine in poisonnut (Strychnos nux vomica) and 1998 Chinese Traditional and Herbal Drugs 29(4): 236-237 -
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