A Synthetic Route to β-Hydroxytyrosine-Derived Tetramic Acids: Total Synthesis of the Fungal Metabolite F-14329

Synthesis and Bioactivity of a Macrocidin B Stereoisomer

A stereoisomer of macrocidin B, a presumed metabolite of the fungus Phoma macrostoma, was synthesized in 18 steps and 2.7% yield from protected l-tyrosine that was N-β-ketoacylated with a fully functionalized octanoyl Meldrum's acid. Dieckmann condensation gave a 3-acyltetramic acid, which was macrocyclized via Williamson etherification between the phenol and epi-bromohydrin termini. This macrocidin B stereoisomer showed a weaker herbicidal effect than macrocidin A and no similar inhibitory effect on biofilms of Staphylococcus aureus.

Stereostructure Clarifying Total Synthesis of the (Polyenoyl)tetramic Acid Militarinone B. A Highly Acid-Labile N-Protecting Group for Amides†

The 5S, 8'R, and 10'R configurations of militarinone B (3), which is a natural product from Paecilomyces militaris, should equal those in its biosynthetic precursor, militarinone C. The configuration at C-1' emerged from syntheses of the militarinone B candidates 1''S- and 1''R-(5S,8'R,10'R)-3 from the building blocks 9, 11, 14, and 15a while introducing TMB as a more acid-labile N-protecting group for β-ketoamides than DMB. Comparisons of 1''S- and 1''R-(5S,8'R,10'R)-3 with natural militarinone B (3; reisolated from Nature) revealed identity versus distinctness.

Synthetic Access to Hydrophilic Tetramate Derivatives of Cysteine

The synthesis, structural, and antibacterial evaluation of bicyclic tetramate derivatives of cysteine rendered hydrophilic with pendant heterocyclic substituents is reported; effective synthetic protocols and antibacterial activity for a small library of polar derivatives were found, and direct evidence for strong metal chelation in these systems was obtained. A computational study has developed a detailed understanding of the controlling factors of the key Dieckmann cyclization step.

A Highly Effective Route to Si-O-Si Moieties through O-Silylation of Silanols and Polyhedral Oligomeric Silsesquioxane Silanols with Disilazanes

A simple and highly practical catalyst-free O-silylation of silanols with commercially available disilazanes has been developed under mild conditions. In the case of polyhedral oligomeric silsesquioxane (POSS) silanols and some other silanols, it was necessary to use catalytic amounts of inexpensive Bi(OTf)₃ as additional catalyst. This efficient chlorine-free protocol involves the synthesis of a wide range of important organosilicon derivatives such as unsymmetrical disiloxanes and functionalized silsesquioxanes.

Stereoselective and Catalytic Synthesis of anti-β-Alkoxy-α-azido Carboxylic Derivatives

Direct addition of a chiral N-azidoacetyl thiazolidinethione to a variety of dialkyl acetals catalyzed by a commercially available and structurally simple nickel(II) complex gives access in good yields and a highly stereocontrolled manner to anti-β-alkoxy-α-azido carboxylic derivatives which, in turn, can be easily converted into a wide array of enantiomerically pure compounds.