Bacterial cell wall protecting groups

In the furanoside field, the introduction of the last two P-arabino units of a hexasaccharide motif from a bacterial cell wall arabinogalactan was achieved by the sulfoxide method with stereocontrol achieved because of the presence of the 2,3-anhydro group (Scheme 4.62) [368], More recently, the direct stereocontrolled synthesis of arabinofuranosides has been achieved by the sulfoxide method with the aid of a 3,5-0-(di-tert-butylsilylene)-protected donor [369]. 

Particularly it became necessary to consider the bacterial membrane. As things stand now, the bacterial cell wall is thought of as an outer skeleton which can be freely traversed by macromolecules and is important for the mechanical structure and protection of the cell. It is made up of polysaccharides and carbohydrate-derived substances, which include some peptide groups. Underneath the cell wall there is the cell membrane, which appears to be the seat of the important physiological functions of assimilation and excretion. Some findings suggest... 

Penicillin imitates D-AIa and binds to the active site of the enzyme, encouraging the OH group of a serine residue to attack the reactive, strained [5-lactam. This same OH group of the same serine residue would normally be the catalyst for the D-Ala-D-Ala cleavage used in the building of the bacterial cell wall. The reaction with penicillin protects the serine and irreversibly inhibits the enzyme. The bacterial cell walls cannot be completed, and the bacterial cells literally burst under the pressure of their contents. Penicillin does not kill bacteria whose cell walls are already complete but it does prevent new bacteria being formed. 

A Lilly group21"3 devised a synthesis of the bacterial cell wall precursor UDP-N-acetylmuramyl-pentapeptide (Park nucleotide) in which deprotection of a 2-(phenylsulfonyl)ethyl ester using a catalytic amount of DBU in dichloro-methane220,221 was an important step in the release of a carboxyl group [Scheme 6,99]. 2-(Methylsulfonyl)ethyl esters have also been cleaved under basic conditions to release a protected carboxylic acid. Scheme 6.100 shows an example from the closing stages of a synthesis of Surugatoxin.222... 

Lysozyme brings about hydrolysis of the bacterial cell wall, specifically, the P-1, 4-glycosidic bonds. Activity toward gram-negative species is limited because of the protective outer cell membrane in this group (Villa, 1996). Lysozyme has no effect on yeasts. 

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