Conduritol tetraacetate

Certain bromoquercitol pentaacetates, treated with zinc-acetic acid, give conduritol tetraacetates (see p. 43). 

Conduritols and inositols are cyclic polyalcohols with significant biological activity. The presence of four stereogenic centers in the stmcture of conduritols allows the existence of 10 stereoisomers. Enzymatic methods have been reported for the resolution of racemic mixtures or the desymmetrization of meso-conduritols. For example, Mucor miehei lipase (MML) showed enantiomeric discrimination between all-(R) and all-(S) stereoisomers ofconduritol E tetraacetate (Figure 6.52). Alcoholysis resulted in the removal of the four acetyl groups ofthe all-(R) enantiomer whereas the all-(S) enantiomer was recovered [141]. 

Figure 6.52 Enzymatic alcoholysis of racemic conduritol E tetraacetate.

The kinetic resolution of C2-symmetric racemic substrate as shown in Scheme 8E.22 requires differentiation between the starting material and the monoalkylated product 113 in addition to the enantiodiscrimination in the ionization step. With a bulky carboxylic acid as nucleophile, the racemic tetraacetate of conduritol B was efficiently resolved under phase-transfer conditions [68]. Further elaboration of the hydrolytically desymmetrized alcohol resulted in the synthesis of the important glycosidase inhibitor, (+)-cyclophellitol. 

Finally for this section, as another asymmetric synthesis of cycliphelitol (1), the synthetic effort of Trost s group will be introduced [52]. Their synthesis was conducted based on the palladium-catalyzed kinetic resolution of racemic conduritol B tetraacetate ( )-94. Since racemic... 

Dangschat and Fischer, in an elegant elucidation of the structure of conduritol (16), a naturally occurring cyclitol, isolated the tetraacetate... 

Conduritol-i/ (33) tetraacetate has been prepared by the reaction of a bromoquercitol pentaacetate (39) with zinc. 

Using Upjohn condition (OsOi-NMO). The utility of the Upjohn protocol for the dihydroxylation was recently demonstrated in the synthesis of bicyclic analogues of pentopyranoses, (-)-anisomycin, trisubstituted y-butyrolactone, 6-bromo-4-(l,2-dihydroxyethyl)-7-hydroxycoumarine (Bhc-diol) as a photoremovable protecting group, 3,4-dihydroxy-2-(3-methylbut-2-enyl)-3,4-dihydronaphthalen-l(2//)-one, benzo-[c]pyrano[3,2-/z]acridin-7-ones, both enantiomers of conduri-tol C tetraacetate and of mei o-conduritol-D-tetraacetate. ... 

Recently, Trost and Hembre reported a concise asymmetric synthesis of (+)-cyclophellitol based on the Pd-catalyzed kinetic resolution of racemic conduritol B tetraacetate using the chiral ligand (R,R)A. Most syntheses have started with enantiomerically pure natural products, notably carbohydrates. Such a strategy normally entails rather a long route. A pivalate was chosen as the carboxylate nucleophile for the resolution because the resultant allyl pivalate was anticipated to ionize much more slowly than the starting material. The tetraacetate ( )-conduritol was synthesized from benzo-quinone the kinetic resolution was carried out using 0.65 equiv of sodium pivalate with 1 mol % of (i7 -C3H5PdCl)2 and 3 mol % of (R,R)-AA in a two-phase system with tetra-hexylammonium bromide as the phase transfer catalyst. 

The diolization of the double bond in this series of reactions appears to be analogous to the diolization of the double bond of conduritol, a cyclohexene-tetrol (see Cyclitol section). When the hexenetetrol above was oxidized directly, the hydroxyls entered cis to the hydroxyls already present and allitol was the chief product similarly, aHo-inositol was obtained on oxidation of o-isopropylideneconduritol diacetate with potassium permanganate. On the other hand, for the two fully acetylated tetrols (acyclic and cyclic), the hydroxyls entered trans to those already present, giving galactitol and mwco-inositol tetraacetate, respectively (p. 284). 

Conduritol B Tetraacetate (F). Compound (IV), 30 g, dissolved in 150 ml of trimethyl phosphite, is heated under reflux for 5 hr under nitrogen. The solution is concentrated under reduced pressure to a syrup and triturated with 100 ml of water. The sticky material crystallizes after a few hours. It is recrystallized from 150 ml of methanol/water 3 2. Yield, 18 g m.p., 85°-89°. 

Competitive inhibition, 4 Concanavalin A, 85,368 binding site, 75 Conduritol B, 369 synthesis of, 373 Conduritol B epoxide, 369 active site labeling, 377-380 labeling with, 370 reaction with /3-glucosidases, 369 synthesis of, 371-376 Conduritol B tetraacetate, synthesis of, 373... 

Di-0-ter -butyldimethylsilyl-3,4-0-isopropylidene-D-glucitol on Swem oxidation then treatment with samarium diiodide gives the L-cA/ro-derivative 68 together with a small amount of the myo-isomer. Compound 68 was further converted into its hexaacetate for characterization purposes as well as into conduritol F tetraacetate. ... 

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