1.Synthetic studies on (-)-lemonomycin: an efficient asymmetric synthesis of lemonomycinone amide.
Wu YC1, Bernadat G, Masson G, Couturier C, Schlama T, Zhu J. J Org Chem. 2009 Mar 6;74(5):2046-52. doi: 10.1021/jo8027449.
Asymmetric synthesis of lemonomycinone amide (2) was accomplished from readily accessible starting materials. Enantioselective alkylation of N-(diphenylmethylene)glycine tert-butyl ester (11) by 5-tert-butyldimethylsilyloxy-2,4-dimethoxy-3-methylbenzyl bromide (10) in the presence of Corey-Lygo's phase transfer catalyst [O-(9)-ally-N-(9'-anthracenylmethyl) cinchonidium bromide, 0.1 equiv] afforded, after chemoselective hydrolysis of the imine function (THF/H(2)O/AcOH), the substituted l-tert-butyl phenylalanate 13 in 85% yield. A Pictet-Spengler reaction of 14 with benzyloxyacetaldehyde (15) provided the 1,3-cis-disubstituted tetrahydroisoquinoline 16 in 85% yield as a single diastereomer. Coupling of hindered secondary amine 16 with amino acid 9 was accomplished under carefully controlled conditions to furnish the amide 22, which was in turn converted to hemiaminal 24. A hafnium triflate catalyzed conversion of hemiaminal to alpha-amino thioether followed by a silver tetrafluoroborate promoted intramolecular Mannich reaction of 26 afforded the tetracycle 27 in excellent overall yields.
2.Lobocyclamide B from Lyngbya confervoides. Configuration and asymmetric synthesis of beta-hydroxy-alpha-amino acids by (-)-sparteine-mediated aldol addition.
MacMillan JB1, Molinski TF. Org Lett. 2002 May 30;4(11):1883-6.
[reaction: see text] Lobocyclamide B, a cyclododecapeptide containing five beta-hydroxy-alpha-amino acid residues, was isolated from Lyngbya confervoides. This is the first reported occurrence of gamma-hydroxythreonine in a natural peptide. Optically active beta-hydroxy-alpha-amino acids required for configurational analysis of the title compound were prepared using a novel (-)-sparteine-mediated asymmetric aldol addition of N-(diphenylmethylene)glycine tert-butyl ester to aldehydes. The method is general for aliphatic and aryl aldehydes and notable for operational simplicity.
3.Molecular design of chiral quaternary ammonium polymers for asymmetric catalysis applications.
Parvez MM1, Haraguchi N, Itsuno S. Org Biomol Chem. 2012 Apr 14;10(14):2870-7. doi: 10.1039/c2ob06909a. Epub 2012 Mar 5.
Repeated reaction between a chiral quaternary ammonium dimer and disodium disulfonate gave a chiral ionic polymer, which showed excellent catalytic activity in the asymmetric benzylation of N-diphenylmethylene glycine tert-butyl ester.
4.Combinatorial design of simplified high-performance chiral phase-transfer catalysts for practical asymmetric synthesis of alpha-alkyl- and alpha,alpha-dialkyl-alpha-amino acids.
Kitamura M1, Shirakawa S, Arimura Y, Wang X, Maruoka K. Chem Asian J. 2008 Sep 1;3(8-9):1702-14. doi: 10.1002/asia.200800107.
A very efficient, chiral phase-transfer catalyst, (S)-2 Db, was prepared by taking advantage of the combinatorial approach from the readily available (S)-1,1'-binaphthyl-2,2'-dicarboxylic acid. This catalyst exhibited high catalytic performance (0.01-0.1 mol %) in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester and N-(p-chlorophenylmethylene)alanine tert-butyl ester relative to other chiral phase-transfer catalysts in current use. This has created a general and highly practical procedure for the enantioselective synthesis of structurally diverse natural and unnatural alpha-alkyl-alpha-amino acids as well as alpha,alpha-dialkyl-alpha-amino acids. A similar simplified catalyst, (S)-2 Fb, is also applicable to the direct asymmetric aldol reaction between glycine Schiff base and aldehydes with moderate syn selectivity and high enantioselectivity.
