Effect of Four Grape Varieties on the Physicochemical and Sensory Properties of Unripe Grape Verjuice.

Verjuice is a sour-tasting juice obtained from the mechanical pressing of unripe grapes. The significance of verjuice as food product includes but not limited to its richness in antioxidant compounds, its usage as an alternative to lemon and vinegar, and also its production which can reduce the losses of lower quality grapes and waste from grape thinning. In this study, a survey for the common Lebanese traditional preparation methods for verjuice was done and physicochemical properties of four Lebanese verjuice varieties Tfayfihi, Baytamoni, Black, and Obeideh along with their sensory evaluation by consumers were studied. Results showed that "Black" grape verjuice has the highest density (1.01 ± 0.003 g/L), titratable acidity (4.51 g/L ± 0.03), total soluble solids (5.38°Brix ± 0.3), and polyphenol content (676.1 mg/L ± 6.8); verjuice processed from the Baytamoni grape variety has the highest browning index (0.432 ± 0.002) and color intensity (1.18 ± 0.007); "Obeideh" grape verjuice has the highest pH (2.55 ± 0.006); and "Tfayfihi" grape verjuice has the highest radical scavenging potential (91.76% ± 0.43) and moisture content (95.85% ± 0.19). Both "Tfayfihi" and "Black" grape verjuice has the highest total suspended solids (40 g/L ± 1.3 and 40 g/L ± 2.9, respectively) among all studied verjuice. There is no difference in taste between the four verjuice varieties which we studied, but there is a color preference for the "Tfayfihi" verjuice. The use of different varieties of grapes in the processing of verjuice affects the physicochemical and sensory properties and results in selection of grape varieties being favorable in the processing of verjuice with respect to factors such as polyphenol content and color of the final product.

N-tosyl-3-azacyclohexyne. Synthesis and chemistry of a strained cyclic ynamide.

The first synthesis of a strained six-membered cyclic ynamide is described. N-Tosyl-3-azacyclohexyne is generated via fluoride-promoted 1,2 elimination under conditions that allow trapping of the strained heterocyclic alkyne in a variety of addition, insertion, and [2 + 2], [3 + 2], and [4 + 2] cycloaddition reactions.

On the proposed structures and stereocontrolled synthesis of the cephalosporolides.

The synthesis of four candidate stereoisomers of cephalosporolide H is described, made possible by a zinc-chelation strategy for controlling the stereochemistry of oxygenated 5,5-spiroketals. The same strategy likewise enables the first stereocontrolled synthesis of cephalosporolide E, which is typically isolated and prepared admixed with its spiroketal epimer, cephalosporolide F.

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals.

A highly efficient synthesis of oxygenated 5,5-spiroketals was performed towards the synthesis of the cephalosporolides. Gold(I) chloride in methanol induced the cycloisomerization of a protected alkyne triol with concomitant deprotection to give a strategically hydroxylated 5,5-spiroketal, despite the potential for regiochemical complications and elimination to furan. Other late transition metal Lewis acids were less effective. The use of methanol as solvent helped suppress the formation of the undesired furan by-product. This study provides yet another example of the advantages of gold catalysis in the activation of alkyne π-systems.

Synthesis of the tricyclic core of aldingenin B by oxidative cyclo-ketalization of an alkyne-diol.

The preparation and selenium-mediated cyclo-ketalization of an alkyne-diol is described as a model study for the synthesis of aldingenin B. The oxidative cyclization is a simplifying transformation for aldingenin B, as it provides a convenient method for generating the tricylic core of the natural product from a functionalized cyclohexane.

A [4 + 4] annulation strategy for the synthesis of eight-membered carbocycles based on intramolecular cycloadditions of conjugated enynes.

A [4 + 4] annulation strategy for the synthesis of eight-membered carbocycles is reported that proceeds via a cascade involving two pericyclic processes. In the first step, the [4 + 2] cycloaddition of a conjugated enyne with an electron-deficient cyclobutene generates a strained six-membered cyclic allene that isomerizes to the corresponding 1,3-cyclohexadiene. In the second step, this bicyclo[4.2.0]octa-2,4-diene intermediate undergoes thermal or acid-promoted 6-electron electrocyclic ring opening to furnish a 2,4,6-cyclooctatrienone. The latter transformation represents the first example of the promotion of 6-electron electrocyclic ring opening reactions by acid.

Stereocontrol of 5,5-spiroketals in the synthesis of cephalosporolide H epimers.

A blueprint for controlling the stereochemistry of oxygenated 5,5-spiroketals using chelation effects is provided. Chelation specifically of zinc salts (other protic and Lewis acids were less effective) between the spiroketal oxygen and an appropriately positioned alcohol group overrides normal biases in the preparation of 5,5-spiroketals, as illustrated by the stereocontrolled synthesis of epimeric cephalosporolide H isomers. This study provides new and valuable information for prescribing the chirality of the stereogenic core of 5,5-spiroketals.

A striking exception to the chelate model for acyclic diastereocontrol: efficient access to a versatile propargyl alcohol for chemical synthesis.

The four-step, asymmetric synthesis of a chiral propargyl alcohol 1 from (R)-pantolactone is described. A key feature of the synthesis is a diastereoselective acetylide addition to a chiral alpha-alkoxy-aldehyde 7, in which unusual Felkin selectivity is observed, despite the potential for chelation control. Crystalline propargyl alcohol 1 is valuable for complex molecule synthesis, and is easy to prepare in multi-gram quantities and high diastereomeric purity.

New strategies for protecting group chemistry: synthesis, reactivity, and indirect oxidative cleavage of para-siletanylbenzyl ethers.

Reported herein is a new entry in the growing arsenal of arylmethyl ether protecting groups. The para-siletanylbenzyl (PSB) ether is electronically similar to the benzyl ether. Cleavage of the PSB ether is accomplished under mild conditions--involving alkaline hydrogen peroxide--that are unique among cleavage protocols for arylmethyl ethers. Furthermore, the PSB group affords the user new flexibility in the implementation of protecting group strategies that revolve around multiple arylmethyl ether protecting groups. In addition to hydrogen peroxide-based cleavage protocols, conversion of a PSB ether into a para-methoxybenzyl (PMB) ether and assembly of a PSB ether from a pre-existing para-bromobenzyl (PBB) ether are described. Finally, a new reagent for installing PSB ethers under neutral "mix and heat" conditions is reported.