Browsing by Subject "chemistry, organic"

Now showing 1 - 5 of 5
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    Burkholdines 1097 and 1229, Potent Antifungal Peptides from Burkholderia ambifaria 2.2N
    (2010) Tawfik, Kamilia A; Jeffs, Peter; Bray, Brian; Dubay, George; Falkinham, Joseph O; Mesbah, Mostafa; Youssef, Diaa; Khalifa, Sherief; Schmidt, Eric W
    Potent antifungal cyclic lipopeptides, burkholdines (Bk), were isolated from a culture of Burkholderia ambifaria 2.2N. Bk-1229 (1) and Bk-1097 (2) are octapeptides comprised of nonproteinogenic amino acids, including beta-hydroxytyrosine, beta-hydroxyasparagine, and a new fatty acyl amino acid. 1 and 2 are fungicidal against a panel of fungi with potencies 2-60-fold better than amphotericin B control.
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    Development of a Strategy for the Asymmetric Synthesis of Polycyclic Polyprenylated Acylphloroglucinols via N-Amino Cyclic Carbamate Hydrazones: Application to the Total Synthesis of (+)-Clusianone
    (2010) Garnsey, Michelle R; Lim, Daniel; Yost, Julianne M; Coltart, Don M
    A broadly applicable asymmetric synthetic strategy utilizing N-amino cyclic carbamate alkylation that provides access to the various stereochemical permutations of a common structural motif found in many polycyclic polyprenylated acylphloroglucinols is described. The utility of this methodology is demonstrated through the first asymmetric total synthesis of the antiviral agent (+)-clusianone.
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    Direct Carbon-Carbon Bond Formation via Soft Enolization: A Biomimetic Asymmetric Mannich Reaction of Phenylacetate Thioesters
    (2010) Kohler, Mark C; Yost, Julianne M; Garnsey, Michelle R; Coltart, Don M
    An asymmetric Mannich reaction of phenylacetate thioesters and sulfonylimines using cinchona alkaloid-based amino (thio)urea catalysts is reported that employs proximity-assisted soft enolization. This approach to enolization is based on the cooperative action of a carbonyl-activating hydrogen bonding (thio)urea moiety and an amine base contained within a single catalytic entity to facilitate intracomplex deprotonation. Significantly, this allows thioesters over a range of acidity to react efficiently, thereby opening the door to the development of a general mode of enolization-based organocatalysis of monocarboxylic acid derivatives.
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    Gold(I)-Catalyzed Amination of Allylic Alcohols with Cyclic Ureas and Related Nucleophiles
    (2010) Mukherjee, Paramita; Widenhoefer, Ross A
    A 1:1 mixture of [P(t-Bu)(2)-o-biphenyl]AuCl and AgSbF6 catalyzes the Intermolecular amination of allylic alcohols with 1-methylimidazolidin-2-one and related nucleophiles that, in the case of gamma-unsubstituted or gamma-methyl-substituted allylic alcohols, occurs with high gamma-regloselectivity and syn-stereoselectivity.
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    Origins of Stereoselectivity in the alpha-Alkylation of Chiral Hydrazones
    (2010) Krenske, Elizabeth H; Houk, KN; Lim, Daniel; Wengryniuk, Sarah E; Coltart, Don M
    Density functional theory calculations and experiment reveal the origin of stereoselectivity in the deprotonation-alkylation of chiral N-amino cyclic carbamate (ACC) hydrazones. When the ACC is a rigid, camphor-derived carbamate, the two conformations of the azaenolate intermediate differ in energy due to conformational effects within the oxazolidinone ring and steric interactions between the ACC and the azaenolate. An electrophile adds selectively to the less-hindered pi-face of the azaenolate. Although it was earlier reported that use of ACC auxiliaries led to a-alkylated ketones with er values of 82:18 to 98:2, B3LYP calculations predict higher stereosclectivity. Direct measurement of the dr of an alkylated hydrazone prior to removal of the auxiliary confirms this prediction; the removal of the auxiliary under the reported conditions can compromise the overall stereoselectivity of the process.