Metabolic glycoengineering has been established as a highly valuable tool to non-destructively investigate glycosylation.[1-3] In previous studies we found that Ac₄ManNAcryl (1) reacts well in the nitrile imine photoclick reaction and not in the DAinv reaction, and that Ac₄ManNCyoc (2) as well as Ac₄ManNCp (3) react very well in the DAinv reaction, thus a orthogonality of these bioorthogonal ligation reactions is possible.[4, 5] To gain better insight into the photoclick reaction and to simplify analytics, two cyclopropene model compounds (CHexNCyoc (4) and CHexNCp (5)) were synthesized. 4 and 5 were reacted with Tet-1 (6) and Tet-2 (7). For 5 both corresponding pyrazolines were obtained in 83 % yields, for 4 TLC monitoring showed no or only marginal reaction occurs. To quantify these findings, a time resolved ¹HNMR spectroscopy study was performed. It was found that 4 reacts to a certain extent with the 6 and 7, but 5 reacts much more readily. DFT calculations underpinned these findings, showing that 5 reacts up to 6 million times faster than 4. The photo-click and the DAinv reaction were applied in MGE using Ac₄ManNCp (8), Ac₄ManNCyoc (9) and Ac₄ManNAcryl (10). For the photoclick reaction nice membrane staining was obtained for 8 and 10, whereas 9 was not labelled, for the DAinv reaction membrane staining was obtained for 8 and 9, but not for 10. The orthogonality between Ac₄ManNCyoc (9) and Ac₄ManNAcryl (10) is therefore proven.
- Dube, D. H.; Bertozzi, C. R., Metabolic oligosaccharide engineering as a tool for glycobiology. Curr Opin Chem Biol 2003, 7 (5), 616-625.
- Keppler, O. T.; Horstkorte, R.; Pawlita, M.; Schmidts, C.; Reutter, W., Biochemical engineering of the N-acyl side chain of sialic acid: biological implications. Glycobiology 2001, 11 (2), 11r-18r.
- Prescher, J. A.; Bertozzi, C. R., Chemical technologies for probing glycans. Cell 2006, 126 (5), 851-854.
- Späte, A.-K.; Busskamp, H.; Niederwieser, A.; Schart, V. F.; Marx, A.; Wittmann, V., Rapid Labeling of Metabolically Engineered Cell-Surface Glycoconjugates with a Carbamate-Linked Cyclopropene Reporter. Bioconjugate Chem. 2014, 25 (1), 147-154.
- Schart, V. F.; Hassenrück, J.; Späte, A.-K.; Dold, J. E. G. A.; Fahrner, R.; Wittmann, V., Triple Orthogonal Labeling of Glycans by Applying Photoclick Chemistry. ChemBioChem 2019, 20 (2), 166-171.