Efficient synthesis of building blocks for branched rhamnogalacturonan I fragments

Mild and General Protocol for Selective Deacetylation of Acetyl/Benzoyl-Protected Carbohydrates

Herein, we report a mild and general protocol for chemoselective deacetylation of mixed acetyl- and benzoyl-protected carbohydrates under mild acidic conditions. The protocol allows quick access to partially protected carbohydrates, which serve as versatile synthetic intermediates during the total synthesis of various mono- and oligosaccharide targets. The applicability of the developed protocol was successfully demonstrated on a range of carbohydrate substrates of various configurations and substitution patterns featuring functionalized aliphatic and aromatic aglycones. The protocol has shown excellent compatibility with the widely used O-anomeric protecting groups, prespacer aglycones, and thioglycoside glycosyl donors.

Cell Wall Polysaccharide Composition of Grafted 'Liberty' Watermelon With Reduced Incidence of Hollow Heart Defect

Grafting watermelon scions to interspecific squash hybrids has been found to increase fruit firmness. Triploid (seedless) watermelon are prone to hollow heart (HH), an internal fruit disorder characterized by a crack in the placental tissue expanding to a cavity. Although watermelon with lower tissue firmness tend to have a higher HH incidence, associated differences in cell wall polysaccharide composition are unknown. Grafting "Liberty" watermelon to "Carnivor" (interspecific hybrid rootstock, C. moschata × C. maxima) reduced HH 39% and increased tissue firmness by 3 N. Fruit with and without severe HH from both grafted and non-grafted plants were analyzed to determine differences in cell wall polysaccharides associated with grafting and HH. Alcohol insoluble residues (AIR) were sequentially extracted from placental tissue to yield water soluble (WSF), carbonate soluble (CSF), alkali soluble (ASF), or unextractable (UNX) pectic fractions. The CSF was lower in fruit with HH (24.5%) compared to those without HH (27.1%). AIRs were also reduced, hydrolyzed, and acetylated for GC-MS analysis of monosaccharide composition, and a portion of each AIR was methylated prior to hydrolysis and acetylation to produce partially methylated alditol acetates for polysaccharide linkage assembly. No differences in degree of methylation or galacturonic and glucuronic acid concentrations were found. Glucose and galactose were in highest abundance at 75.9 and 82.4 μg⋅mg^-1 AIR, respectively, followed by xylose and arabinose (29.3 and 22.0 μg⋅mg^-1). Mannose was higher in fruit with HH (p < 0.05) and xylose was highest in fruit from grafted plants (p < 0.05). Mannose is primarily found in heteromannan and rhamnogalacturonan I side chains, while xylose is found in xylogalacturonan or heteroxylan. In watermelon, 34 carbohydrate linkages were identified with galactose, glucose, and arabinose linkages in highest abundance. This represents the most comprehensive polysaccharide linkage analysis to date for watermelon, including the identification of several new linkages. However, total pectin and cell wall composition data could not explain the increased tissue firmness observed in fruit from grafted plants. Nonetheless, grafting onto the interspecific hybrid rootstock decreased the incidence of HH and can be a useful method for growers using HH susceptible cultivars.

Temporary ether protecting groups at the anomeric center in complex carbohydrate synthesis

The synthesis of a carbohydrate building block usually starts with introduction of a temporary protecting group at the anomeric center and ends with its selective cleavage for further transformation. Thus, the choice of the anomeric temporary protecting group must be carefully considered because it should retain intact during the whole synthetic manipulation, and it should be chemoselectively removable without affecting other functional groups at a late stage in the synthesis. Etherate groups are the most widely used temporary protecting groups at the anomeric center, generally including allyl ethers, MP (p-methoxyphenyl) ethers, benzyl ethers, PMB (p-methoxybenzyl) eithers, and silyl ethers. This chapter provides a comprehensive review on their formation, cleavage, and applications in the synthesis of complex carbohydrates.

Synthesis of Two Tetrasaccharide Pentenyl Glycosides Related to the Pectic Rhamnogalacturonan I Polysaccharide

The synthesis of two protected tetrasaccharide pentenyl glycosides with diarabinan and digalactan branching related to the pectic polysaccharide rhamnogalacturonan I is reported. The strategy relies on the coupling of N-phenyl trifluoroacetimidate disaccharide donors to a common rhamnosyl acceptor. The resulting trisaccharide thioglycosides were finally coupled to an n-pentenyl galactoside acceptor to access the two protected branched tetrasaccharides.