Classics In Total Synthesis of Oligosaccharides and Glycoconjugates

More precisely, the strategical problems inherent to the total synthesis of Nod factors are as follows  

The four primary hydroxyl groups have to be carefully differentiated the presence of a sulfate group and, in compound 2, of an additional acetate, forces the introduction of suitable temporary protecting groups on the primary positions. 

Similarly, one amino group has also to be differentiated from the others. 

but not least, the presence of double bonds in the final product precludes the classical use of hydrogenation conditions, subsequent to the introduction of the unsaturated chain. This means for example that the very classical benzyl ether cannot be used as a protecting group in the last steps. This kind of problem is similar to the one met in the synthesis of sphingoglycolipids where a double bound is also present in the sphingosine moiety. 

The key protected tetrasaccharide to be synthesized in this approach is compound 

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