Here we report the preparation of various synthetic lipid-linked oligosaccharides (LLOs) and their phosphonate analogs. These LLOs act as glycosyl donors in biochemical studies of enzymes involved in protein glycosylation, such as oligosaccharyl flippases (PglK)^[1] and oligosaccharyl transferases (OSTs),^[2,3] while their phosphonate analogs can be used as inhibitors of the same enzymes. The LLOs were obtained in 16 to 31 steps in a convergent synthesis involving the coupling of a lipid phosphate with a glycosyl phosphate or phosphonate. Inspired by known procedures,^[4] we designed an accelerated synthesis of novel α-saturated chiral C₂₀- and C₂₅-polyprenyl phosphates, essential to obtain LLOs reacting with eurakyotic OSTs, using a stereoselective olefination as the key step.^[5] Furthermore, we established the synthesis of chitobiose phosphonates from N-acetyl-D-glucosamine involving as key steps C₁-allylation, β-1,4 glycosylation, condensation with diethyl phosphite and deoxygenation.^[6] The final products were obtained in 20-50 mg scale in pure form suitable for biochemical and structural studies.

[1] Camilo Perez, Sabina Gerber, Jérémy Boilevin, Monika Bucher, Tamis Darbre, Markus Aebi, Jean-Louis Reymond, Kaspar Locher, Nature, 2015, 524, 433-438.
[2] Christian Lizak, Sabina Gerber, Shin Numao, Markus Aebi, Kaspar Locher, Nature, 2011, 474, 350-355.
[3] Christian Lizak, Sabina Gerber, Gaëlle Michaud, Mario Schubert, Yao-Yun Fan, Monika Bucher, Tamis Darbre, Markus Aebi, Jean-Louis. Reymond, Kaspar Locher, Nat. Commun., 2013, 4, 2627-2637.
[4] Feng Liu, Balakumar Vijayakrishnan, Amirreza Faridmoayer, Thomas Taylor, Thomas Parsons, Gonçalo Bernardes, Michael Kowarik, Benjamin Davis, J. Am. Chem. Soc., 2014, 136, 566-570.
[5] Xinggao Fang, Barbara Gibbs, James Coward, Bioorg. Med. Chem. Lett., 1995, 5, 2701-2706. 
[6] Cheng-Kun Lin, Kuo-Ting Chen, Chia-Ming Hu, Wen-Yi Yun, Wei-Chieh Cheng, Chem. Eur. J., 2015, 21, 1-10.