Synthesis and Biological Evaluation of 6-[(1R)-1-Hydroxyethyl]-2,4a(R),6(S),8a(R)-tetrahydropyrano-[3,2-b]-pyran-2-one and Structural Analogues of the Putative Structure of Diplopyrone

Synthesis of Pyranopyrans Related to Diplopyrone and Evaluation as Antibacterials and Herbicides

Stereoselective syntheses of new pyranopyrans that are related to the natural product diplopyrone, which is a phytotoxin implicated in cork oak decline, have been achieved from carbohydrate starting materials in two approaches that are based on C-glycosides as key intermediates. A C-alkynyl glycoside prepared by Ferrier rearrangement was used as the precursor to a new pyranopyran alkyne that showed potent antibacterial activity against the common bacterial pathogen Edwardsiella ictaluri that causes enteric septicemia in catfish. The C-alkynyl glycoside also showed herbicidal activity. New bioassay data for the pyranopyran nitrile (4aR,6S,8aR)-6-cyano-6,8a-dihydropyrano-[3,2-b]pyran-2(4aH)-one, the most potent of the pyranopyrans synthesized to date, were obtained in greenhouse studies that revealed additional herbicidal activity. Other new analogues that were synthesized included desmethylpyranopyrans that were prepared by Isobe C-alkynylation-rearrangement/reduction and RCM-based pyranopyran construction. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study highlight the importance of substituents on the nonlactone ring and demonstrate the potential of such compounds as antibiotics and herbicides.

Synthesis and crystal structure of (2S,4aR,8aR)-6-oxo-2,4a,6,8a-tetra-hydro-pyrano[3,2-b]pyran-2-carboxamide

The pyran-opyran amide (2S,4aR,8aR)-6-oxo-2,4a,6,8a-tetra-hydro-pyrano[3,2-b]pyran-2-carboxamide, C9H9NO4, 3, was prepared by a chemoselective hydration of the corresponding nitrile, 2, using a heterogeneous catalytic method based on copper(II) supported on mol-ecular sieves, in the presence of acetaldoxime. Compound 3 belongs to a new class of pyran-opyrans that possess anti-bacterial and phytotoxic activity. Crystallographic analysis of 3 shows a bent structure for the cis-fused bicyclic pyran-opyran, similar to nitrile 2. Evidence of an intra-molecular hydrogen bond involving the amide group and ring oxygen was not observed; however, two separate inter-molecular hydrogen-bonding inter-actions were observed between the amide hydrogen atoms and adjacent carbonyl oxygen atoms along the b- and a-axis directions. The latter inter-action may also be supported by an inter-molecular C-H⋯O hydrogen bond. The lattice is filled out by close-packed layers of this hydrogen-bonded network along the c-axis direction, related from one to the next by a 21 screw axis.

Synthesis of Bradyrhizose from d-Glucose

We describe the synthesis of the unusual bicyclic sugar bradyrhizose in 14 steps and a 6% overall yield from d-glucose. The synthesis involves the elaboration of a trans-fused carbocyclic ring onto the preexisting glucopyranose framework followed by adjustment of the oxidation levels. Key steps include radical extension of the glucopyranose side chain, ring closing metathesis, allylic oxidation, Luche reduction, hydroxy-directed epoxidation, and acid-catalyzed epoxide opening at the more substituted position.

Synthesis of Sialyl LewisX Glycomimetics Bearing a Bicyclic 3- O,4- C-Fused Galactopyranoside Scaffold

Reported herein is the synthesis of sialyl Lewis^X analogues bearing a trans-bicyclo[4.4.0] dioxadecane-modified 3- O,4- C-fused galactopyranoside scaffold that locks the carboxylate pharmacophore in either the axial or equatorial position. This novel series of bicyclic galactopyranosides are prepared through a stereocontrolled intramolecular cyclization reaction that has been evaluated both experimentally and by density functional theory calculations. The cyclization precursors are obtained from β-d-galactose pentaacetate in a nine-step sequence featuring a highly diastereoselective equatorial alkynylation and Cu(I) catalyzed formation of the acetylenic α-ketoester moiety. Preliminary biological evaluations indicate improved activity as P-selectin antagonists for the axially configured analogues as compared to their equatorial counterparts.