Cycloheptanic sugar mimetics, bridging the gap in the homologous series of carbocyclic analogues

Synthesis of novel seven-membered carbasugars and evaluation of their glycosidase inhibition potentials

Here, we report the synthesis of five novel seven-membered carbasugar analogs. We adopted a chiral-pool strategy starting from the cheap and readily available d-mannitol to synthesize these ring-expanded carbasugars. Apart from several regioselective protecting group manipulations, these syntheses involved Wittig olefination and ring-closing metathesis as the key steps. We observed an unprecedented deoxygenation reaction of an allylic benzyl ether upon treatment with H₂/Pd during the synthesis. Preliminary biological evaluation of the carbasugars revealed that these ring expanded carbasugars act as inhibitors of various glycosidases. This study highlights the importance of the synthesis of novel ring expanded carbasugars and their biological exploration.

Here, we report the synthesis of five novel seven-membered carbasugar analogs.

Stereocontrolled Debenzylative Cycloetherification Reaction as a Route to Enantiopure C-Furanosides with Amino Substituents in the Side Chain

A highly efficient methodology of the preparation of synthetically important tetrahydrofuran derivatives with an amino substituent in the side chain is reported. This process is based on the stereocontrolled debenzylative cycloetherification (DBCE) reaction applied for chirons from the d-gluco- and d-manno-series and provides derivatives with new stereogenic centers. The influence of the electron-withdrawing group (EWG), present in the acyclic substrates with the mesyl leaving group, on the reactivity in the DBCE reaction was investigated both “in the flask” and by density functional theory (DFT) calculations. It was demonstrated that tetrahydrofuran derivatives with the benzoxime group (EWG = CHNOBn) are very good candidates for the subsequent highly stereoselective Grignard reaction.

An efficient synthesis of chloro-aminocyclooctanediol and aminocyclooctanetriol: an unexpected acetolysis product

A concise and efficient synthesis of 2-amino-4-chlorocyclooctanediol, aminocyclooctanetriols and unusual 1,3-hydride shift during the ring opening reaction of epoxide is described.

Synthesis of Cycloheptane-1,2,3,4-tetraols as Cyclitol Mimetics

Acidic hydrolysis and acetylation of epoxidation products 11a/b of 1,4-diacetoxy-2-cycloheptene afforded unsymmetrical 1,2,3,4-tetraacetoxycycloheptane (12). OsO4-cis-hydroxylation and acetylation of 1,4-diacetoxy-2-cycloheptene gave two symmetrical 1,2,3,4-tetraacetoxycycloheptanes (14/15). Deacetylation of 1,2,3,4-tetraacetoxy cycloheptanes gave cycloheptane-1,2,3,4-tetraols as cyclitol mimetics.

Synthesis of (±)-Sundiversifolide Based on Lewis Acid-Mediated Claisen Rearrangement

A new and concise synthesis of (+/-)-sundiversifolide (1), an allelopathic bisnor-sesquiterpene lactone isolated from germinating sunflower (Helianthus annuus L.) seeds, was achieved by employing Lewis acid-mediated Claisen rearrangement as the key step.

Synthesis of 4-membered carbasugars by way of stereoselective SmI2-mediated aldehyde-alkene cyclization

A stereodivergent synthesis of the first examples of 4-membered carbasugars has been achieved from vitamin C by way of an efficient intramolecular SmI2-mediated aldehyde-alkene coupling. In this key step, cylobutanes with four contiguous asymmetric centers are generated with a high level of stereocontrol.

Design and synthesis of novel carbocyclic versions of 2'-spirocyclopropyl ribonucleosides as potent anti-HCV agents

The discovery of 2'-spirocyclopropyl-ribocytidine as a potent inhibitor of RNA synthesis by NS5B (IC(50) = 7.3 μM), the RNA polymerase encoded by hepatitis C virus (HCV), has led to the synthesis and biological evaluation of carbocyclic versions of 2'-spiropropyl-nucleosides from cyclopentenol 6. Spirocyclopropylation of enone 7 was completed by using (2-chloroethyl)-dimethylsulfonium iodide and potassium t-butoxide to form the desired intermediate 9a. The synthesized nucleoside analogues, 18, 19, 26, and 27, were assayed for their ability to inhibit HCV RNA replication in a subgenomic replicon Huh7 cell line. The synthesized cytosine nucleoside 19 showed moderate anti-HCV activity (IC(50) = 14.4 μM).

Total synthesis of optically active lycopladine A by utilizing diastereoselective protection of carbonyl group in a 1,3-cyclohexanedione derivative

We successfully synthesized two enantiomers of bicyclic enones, (7R,7aR)- and (7S,7aS)-9, from the hemiacetal 2a, which we first synthesized from the symmetrical diketone 1a via diastereoselective carbon-oxygen bond formation between one of the carbonyl groups and the chiral alcohol on the C2 side chain in a 2,2-disubstituted 1,3-cycloalkanedione derivative. We also report the total synthesis of natural (+)-lycopladine A [(+)-6] from (7R,7aR)-9 and the formal synthesis of unnatural (-)-lycopladine A [(-)-6] from (7S,7aS)-9.

From D-glucose to enantiomerically pure cycloctanoses. The glycosidase inhibitory capacity of medium-ring carbasugars

Exhaustive dihydroxylation of the pair of cyclooctadienols consisting of 4 and 5, which are available in enantiomerically pure form from d-glucose, resulted in the formation of two diastereomeric tetraols in each case. The difference in polarity of the 6/7 and 8/9 pairs facilitated their chromatographic separation. Ensuing acetylation and PMB deprotection allowed for the assignment of relative (and ultimately absolute) stereochemistry to the resulting monohydric alcohols on the basis of J(HH) analysis of their (1)H NMR spectra. The highly functionalized exomethylenecyclooctanes 14-17, which were derived by periodinane oxidation and Wittig olefination, were further elaborated by hydroboration and global deprotection. The eight members of the cyclooctanose family of carbasugars and their precursor intermediates consistently showed patterns of J(HH) values in line with the contiguous stereochemical relationships. Also assayed was their specific inhibitory behavior toward glycosidases.

Stereocontrolled synthesis of D- and L-beta-rhamnopyranosides with 4-O-6-S-alpha-cyanobenzylidene-protected 6-thiorhamnopyranosyl thioglycosides

The synthesis of both enantiomers of a 4-O-6-S-alpha-cyanobenzylidene-protected 6-thiorhamnopyranosyl thioglycoside is described starting from D-mannnose and L-arabinose derivatives for the D- and L-series, respectively. This donor is effective in the preparation of the corresponding beta-glycosides using the 1-benzenesulfinyl piperidine/trifluoromethanesulfonic anhydride protocol. Following desulfurization and concomitant debenzylation with Raney nickel, the so-formed 6-thio-beta-mannosides are converted in high yield to the beta-rhamnopyranosides.

Highly stereoselective synthesis of C-vinyl furanosides through acid-catalyzed S(N)2 inversion at the C-3 position of 1,2-dideoxy-hept-1-enitols

A highly stereoselective synthesis of C-vinyl furanosides through the S(N)2 inversion at the C-3 position of the 1,2-dideoxy-hept-1-enitols is disclosed. Treatment of the 1,2-dideoxy-hept-1-enitols with diphenylammonium trifluoromethanesulfonate as the acid catalyst produced the C-vinyl furanosides (3,6-anhydro-1,2-dideoxy-hept-1-enitol derivatives) via a subsequent S(N)2 intramolecular debenzyloxyation-cycloetherification reaction at the C-3 position.

From Common Carbohydrates to Enantiopure Cyclooctane Polyols and Glycomimetics via Deoxygenative Zirconocene Ring Contraction

D-Arabinose and D-glucose are transformed into the identical vinyl furanoside, whose role is to serve as the precursor to enantiopure cyclooctadienone 6. The key steps of this relay involve a zirconocene-promoted ring contraction and [3,3] sigmatropic rearrangement of an enynol. Subsequently defined are convenient synthetic routes to several cyclooctane-1,2,3-triols, 1,2,3,4,5-pentaols, and structurally related glycomimetics.

The first synthesis of substituted azepanes mimicking monosaccharides: a new class of potent glycosidase inhibitors

The synthesis of the first examples of seven-membered ring iminoalditols, molecules displaying an extra hydroxymethyl substituent on their seven-membered ring compared to the previously reported polyhydroxylated azepanes, has been achieved from d-arabinose in 10 steps using RCM of a protected N-allyl-aminohexenitol as a key step. While the (2R,3R,4R)-2-hydroxymethyl-3,4-dihydroxy-azepane 10, a seven-membered ring analogue of fagomine, is a weak inhibitor of glycosidases, the (2R,3R,4R,5S,6S)-2-hydroxymethyl-3,4,5,6-tetrahydroxy-azepane 9 selectively inhibits green coffee bean alpha-galactosidase in the low micromolar range (Ki = 2.2 muM) despite a D-gluco relative configuration.