The occurrence of N-glycans with a bisecting GlcNAc modification on glycoproteins has many implications in developmental and immune biology. However, these particular N-glycans are difficult to obtain either from nature or through synthesis. We have developed a flexible and general method for synthesizing bisected N-glycans of the complex type by employing modular TFAc-protected donors for all antennae. The TFAc-protected N-glycans are suitable for the late introduction of a bisecting GlcNAc. This integrated strategy permits for the first time the use of a single approach for multiantennary N-glycans as well as their bisected derivatives via imidates, with unprecedented yields even in a one-pot double glycosylation. With this new method, rare N-glycans of the bisected type can be obtained readily, thereby providing defined tools to decipher the biological roles of bisecting GlcNAc modifications.

A novel, highly stereocontrolled, and very flexible synthetic access to biologically relevant trideoxypropionate building blocks in optically pure form has been developed. On the basis of a three-step sequence comprising a thermal oxy-Cope rearrangement, an iridium-catalyzed hydrogenation, and an auxiliary-controlled enolate methylation, trideoxypropionates with easily adjustable relative configuration were synthesized in excellent yields. In addition, the functionalized end groups allow for chemoselective manipulations and further elongation of the chain. The underlying strategy constitutes the first noniterative process for the assembly of polydeoxypropionates and has further been applied in total syntheses of the pheromones (+)-vittatalactone and (+)-norvittatalactone, which had been isolated from the striped cucumber beetle Acalymma vittatum.

A short sequence comprising an oxy-Cope rearrangement, iridium-catalyzed hydrogenation, and enolate methylation provides trideoxypropionates with excellent diastereocontrol. A straightforward synthesis of the cucumber beetle pheromone (+)-vittatalactone illustrates this new strategy.

A modular set of oligosaccharide building blocks was developed for the synthesis of multiantennary N-glycans of the complex type, which are commonly found on glycoproteins. The donor building blocks were laid out for the elongation of a core trisaccharide acceptor (beta-mannosyl chitobiose) conveniently protected with a single benzylidene moiety at the beta-mannoside. Through two consecutive regio- and stereoselective couplings the donors gave N-glycans with three to five antennae in high yields. Due to the consistent protection group pattern of the donors the deprotection of the final products can be performed by using a general reaction sequence.