Repository logo

1980-1999

Permanent URI for this collection

https://hdl.handle.net/10217/100536

Browse

Browsing 1980-1999 by Subject "Amino acids -- Synthesis"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    The asymmetric synthesis of amino acids via electrophilic glycinates
    (Colorado State University. Libraries, 1987) Sinclair, Peter John, author; Williams, Robert M., advisor
    A new asymmetric synthesis of α-monosubstituted-α-amino acids using D- and L-erythro-4-benzy loxycarbonyl-5,6-diphenyl-2,3,5,6-tetrahydro-1,4-oxazin-2-ones 108 as amino acid templates is described. Bromination of 108 with NBS generates the key electrophilic glycinate 132 which couples with a variety of carbon nucleophiles with high diastereoselectivity to afford the amino acid precursors 134. Catalytic hydrogenation of homologated heterocycles 134 directly furnishes the zwitterionic α-amino acids in high enantiomeric excess. Dissolving metal reduction of 134 permits the preparation of unsaturated amino acids while use of erythro-4-t-butoxycarbonyl-5,6-diphenyl-2,3,5,6-tetrahydro-1,4-oxazin-2-one 160 allows the direct preparation of t-BOC protected α-amino acids. The synthetic approaches to a number of biologically interesting amino acids are described and mechanistic aspects of the coupling reaction are discussed.
  • Thumbnail Image
    ItemOpen Access
    The asymmetric synthesis of amino acids via glycine enolates
    (Colorado State University. Libraries, 1991) Im, Myeong-Nyeo, author; Williams, Robert M., advisor
    The enolates derived from the optically active D-e rythro-4- (tertbutyloxycarbonyl)-5,6-di phenyl-2,3,5,6-tetrahydro-4H-1,4-oxazin-2-one (166a) and D- and L-erythro-4-(benzyloxycarbonyl)-5,6-diphenyl-2,3,5,6- tetrahydro-4H-1,4-oxazin-2-ones (167a/b) efficiently couple with alkyl halides to afford the corresponding anti-α-monosubstituted oxazinones. The enolate alkylation of the a-monosubstituted oxazinones provides the corresponding α-disubstituted oxazinones. Dissolving-metal reduction of the homologated oxazinones allows the direct preparation of t-BOC protected α-amino acids. In the case of dissolving metal-reducible functionality, hydrogenation over a Pd° catalyst furnishes the zwitterionic amino acids. By employing this protocol the syntheses of complex amino acids such as 2-(tert-butyloxycarbonyl)amino-6-(p-methoxybenzyI)thionohexanoic acid and 2,6-diamino-6-hydroxymethylpimelic acid are discussed.
  • Thumbnail Image
    ItemOpen Access
    The asymmetric synthesis of arylglycines
    (Colorado State University. Libraries, 1992) Hendrix, James A., author; Williams, Robert M., advisor
    The asymmetric synthesis of several arylglycines is discussed. Several methods for the coupling of an aromatic group to the chiral bromoglycinates (171, 172) were developed. It was found that the cuprate and Friedel-Crafts couplings provided the desired aryl-coupled glycinates in the greatest yield with excellent selectivity. An oxidative protocol was employed to unmask the oxazinone chiral auxiliary which provided the desired free α-amino acids. A reductive deprotection method was also employed in two unique cases which efficiently gave the arylglycine products. The % ee's ranged from 82 to 94 %. This methodology was further utilized in an approach to the asymmetric synthesis of the bis-arylglycine, actinoidic acid. This study explored the scope of the Stille biphenyl cross-coupling reaction and produced methodology for the synthesis of biphenyl amino acid precursors.