Synthesis of an Aminooxy Derivative of the Tetrasaccharide Repeating Unit of <italic>Streptococcus dysgalactiae</italic> 2023 Polysaccharide for a PS A1 Conjugate Vaccine

A highly efficient and stereocontrolled synthesis of an aminooxy derivative of the tetrasaccharide repeating unit of a rhamnose-rich polysaccharide isolated from the cell envelop of bovine mastitis Streptococcus dysgalactiae 2023 is reported for the first time. The synthesis was accomplished utilizing a stereoselective and convergent [2 + 2] glycosylation strategy inclusive of a disaccharide Schmidt donor and an inclusive rhamnose disaccharide acceptor. The synthetic aminooxy tetrasaccharide was conjugated to T-cell stimulating immunogen PS A1 from Bacteroides f ragilis ATCC 25285/NCTC 9343 via a physiologically stable oxime linkage to furnish the first semisynthetic bacterial-based immunogen construct targeting S. dysgalactiae 2023. The synthetic tetrasaccharide was assembled in 19 steps with a ∼5.0% overall yield. ■ INTRODUCTION Bovine mastitis is an infection of the bovine mammary gland caused by a small cohort of bacteria. Among more than 135 identified causative microorganisms for mastitis, only five have been recognized as major contributing agents including Streptococcus dysgalactiae, Streptococcus uberis, Streptococcus agalactiae, Staphylococcus aureus and Escherichia coli. As a consequence of bacterial invasion and proliferation in the udder, released toxins and enzymes from bacteria induce inflammatory responses, which result in mastitis that can be categorized as either clinical or subclinical. Irrespective of the category of disease, the aftermath is a negative impact on the quality and quantity of milk production by infected cows resulting in ∼$2 billion economic loss each year for the dairy industry. One of the more potent mastitis agents, out of the 5 listed above, is the α-hemolytic Lancefield group C pathogen S. dysgalactiae also known as a contagious and environmental pathogen that can be transmitted via infected udders, manure, and other organic matter including bedding and can survive in the tonsils, mouth and vagina during nonlactating periods. Other than bovine mastitis, S. dysgalactiae is identified to cause toxic shock like syndrome in cattle, bacteremia in dogs, polyarthritis in lambs, severe septicemia and systemic granulomatous inflammatory disease in fish. Antibiotics for treatment of mastitis disease can lead to contaminated milk, which is considered a growing threat toward human health. In cases of subclinical mastitis, where no visible signs of infection are noticeable, the infection will still result in bacteria contaminated milk. This includes unpasteurized dairy products, which represents yet another human health risk. Although Lancefield group C pathogens are mainly considered as animal pathogens, several human maladies have been diagnosed to include glomerulonephritis, puerperal sepsis, bacterial endocarditis, cellulitis, bronchitis, arthritis, toxic shock like syndrome, prosthetic joint infection, pneumonia, osteomyelitis, bacterial endocarditis, and fatal neonatal and adult Received: January 27, 2016 Published: May 5, 2016 Article