Azospirillum brasilense is a plant root-colonizing bacterium that exerts beneficial effects on the growth of agricultural crops (Lerner, Castro-Sowinski, Valverde, Lerner, Dror, Okon & Burdman, 2009). Azospirillum brasilense is routinely found in the plant rhizosphere of crop plants and agricultural lands as well as from grasses and cereals. It has a preference for plant roots instead of open soil. Polysaccharides of bacterium play an important role in its interactions with plant roots. It colonizes the surface of plant roots through attachment and anchoring. A. brasilense Sp7 carries several genes involved in synthesis and export of cell surface polysaccharides. Azospirillum fix the nitrogen in the soil and produces several vitamins and phytohormones to promote crop production. It has properties against the development of bacterial diseases or promoting disease resistance on rice crops (Lerner, Castro-Sowinski, Valverde, Lerner, Dror, Okon & Burdman, 2009).
The intense use of chemicals for the treatment of plant diseases leads to environmental and health risks. Biological control based on plant growth promoting bacteria is the most reasonable approach for the protection of crops against pathogens. Azospirillum brasilense fixes nitrogen in the soil and promotes the overall crop production. It promotes disease resistance on rice crops and the resistance against development of bacterial diseases. The development of chemical synthesis allows access to the required tetrasaccharide that natural sources are depended on (Mandal, Dhara & Misra, 2014).
Biological plant-growth promoting agents are becoming more of a method for improving crop production and minimize the hazards of chemical fertilities. The development of chemical syntheses requires access to tetrasaccharide. In the initial stage of the interactions with plant roots, large quantities of the lipopolysaccaride or its repeating unit are required. As its glycoside, the O-specific polysaccharide of the lipopolysaccahride of Azospiriillum brasilense sp7 strain is correlated to the chemical synthesis of tetrasacahrride repeating unit (Mandal, Dhara & Misra, 2014). The figure below shows the chemical synthesis of the tetrasaccharide-repeating unit corresponding to the O-specific polysaccharide of the lipopolysaccharide of Azospirillum brasilense Sp7 strain as its 2-aminoethyl glycoside.
Stereoselective glycosylation of the disaccharide with the thioglycoside led to the formation of the desired tetrasaccharide. The one pot reaction sequence for this glycosylation and the removal of the methoxybenzyl group were the points of this synthesis (Mandal, Dhara & Misra, 2014). Glycosylation is important for the cell attachment to the extracellular matrix and protein interactions in the cell. It is defined as the attachment of sugar meoieties to proteins and is an also a posttranslational modification that provides greater diversity than other modifications (Lerner, Castro-Sowinski, Valverde, Lerner,...