Rational design, synthesis, and reactivity of lactendiynes, a new class of cyclic enediynes ortho-fused with the β-lactam ring

The first total synthesis of cytopiloyne, an anti-diabetic, polyacetylenic glucoside

The first total synthesis of cytopiloyne 1, a novel bioactive polyacetylenic glucoside isolated from the extract of Bidens pilosa, is described. The structure of cytopiloyne was determined to be 2-β-D-glucopyranosyloxy-1-hydroxytrideca-5,7,9,11-tetrayne by using various spectroscopic methods, but the chirality of the polyyne moiety was unknown. Herein, the convergent synthesis of two diastereomers of cytopiloyne by starting from commercially available 4-(2-hydroxyethyl)-2,2-dimethyl-1,3-diozolane is described. The synthetic sequence involved two key steps: stereoselective glycosylation of the glucosyl trichloroacetimidate with 1-[(4-methoxybenzyl)oxy]hex-5-yn-2-ol to give the desired β-glycoside and the construction of the glucosyl tetrayne skeleton by using a palladium/silver-catalyzed cross-coupling reaction to form the alkyne-alkyne bond, the first such use of this reaction. Comparison between the observed and published characterization data showed the 2R isomer to be the natural product cytopiloyne.

Synthetic Studies Aimed at (−)-Cochleamycin A. Evaluation of Late-Stage Macrocyclization Alternatives

An efficient route to the fully functionalized ABC ring systems of the unnatural enantiomer of cochleamycin A was developed. L-(-)-Malic and L-(-)-ascorbic acids served well as starting materials for the two building blocks used to construct an (E,Z,E)-1,6,8-nonatriene intermediate. The AB part structure was assembled by way of a stereocontrolled intramolecular Diels-Alder cycloaddition via adoption of an endo transition state. From this vantage point, two general pathways were subsequently explored as to their suitability for elaboration of the CD rings. Initially examined was a protocol involving 10-membered carbocycle construction. When this approach was demonstrated not to be workable, attention was directed to 10-membered macrolactonization as an alternative tactic. Although assembly of the C-ring in this manner was easily achieved, ultimate closure of the six-membered ring to form ring D remains an unsolved problem.

Tetrahydroxy 10-Membered Cyclic Enediynes

The preparation of cyclic 10-membered tetrahydroxy enediynes is reported. The synthesis starts from tartaric acid and allows the control of the relative stereochemistry. Acetal protection of the 2,3-hydroxy groups stabilizes the enediyne during synthesis. Removal of the cyclic protecting group with EtSH/TFA transforms the stable compounds into reactive enediynes, and the rate constants of their cyclization were determined in benzene and water. The cytoxicity of the activated compounds was assayed against tumor cells in vitro, but the growth inhibitory effect was weak compared to cisplatin.

Synthesis and structure of a stabilized 10-membered cyclic enediyne

The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification.

Synthesis and antiviral activity of monobactams inhibiting the human cytomegalovirus protease

A series of monobactam inhibitors of HCMV (N(o)) protease bearing a heterocycle linked by a methylene group at C-4 is described. Inhibitors containing a heterocycle such as a 2-furyl, 2-thiophenyl, 4-methyl-2-tetrazole and 2-benzothiazole were found to be active in a plaque reduction assay. Furthermore, 2-benzothiazole derivatives were shown to inhibit the HCMV protease activity inside cells by using a cell transfection assay, indicating that their antiviral activity in the plaque reduction assay could be attributed to protease inhibition.