title: Hydrophobic substituent effects on proline catalysis of aldol reactions in water.
abstract: Derivatives of 4-hydroxyproline with a series of hydrophobic groups in well-defined orientations have been tested as catalysts for the aldol reactions. All of the modified proline catalysts carry out the intermolecular aldol reaction in water and provide high diastereoselectivity and enantioselectivity. Modified prolines with aromatic groups syn to the carboxylic acid are better catalysts than those with small hydrophobic groups (1a is 43.5 times faster than 1f). Quantum mechanical calculations provide transition structures, TS-1a(water) and TS-1f(water), that support the hypothesis that a stabilizing hydrophobic interaction occurs with 1a.
authors.affiliation: Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, Pennsylvania 19122, United States.
authors.forename: Qingquan
authors.initials: Q
authors.lastname: Zhao
authors.forename: Yu-hong
authors.initials: YH
authors.lastname: Lam
authors.forename: Mahboubeh
authors.initials: M
authors.lastname: Kheirabadi
authors.forename: Chongsong
authors.initials: C
authors.lastname: Xu
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.forename: Christian E
authors.initials: CE
authors.lastname: Schafmeister
mesh_terms: D002384:Catalysis; D057927:Hydrophobic and Hydrophilic Interactions; D006909:Hydroxyproline / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D011392:Proline; D006909:Hydroxyproline