[Zurück]

M. Draskovits, C. Stanetty, H. Kalaus, M.D. Mihovilovic:
"N Hetereocyclic carbene controlled dehomologation of aldoses - development and application of a quantification method for the rapid screening of conditions and catalysts";
Poster: 15th European Training Course on Carbohydrates, Wageningen; 24.06.2018 - 28.06.2018.

Carbohydrates are regularly referred to as the Nature´s largest chiral pool, however, only a comparably small set of representatives is actually readily available. Thus, in our research we aim to develop new synthetic methodology for the interconversion of carbohydrate derivatives, focusing on the aldehyde moiety as uniting feature.[1] In our current study, we investigate the organocatalytic anomeric activation with N-heterocyclic carbenes (NHCs) as promising highly carbonyl selective reagent.
Based on the recently published sacrificial degradation of aldoses forming nucleophilic formaldehyde equivalents[2], we are aiming to achieve a controlled NHC catalyzed dehomologation of carbohydrate derivatives. We are investigating this new and complex transformation - putatively based on retro-benzoin and Stetter-type reaction steps - in great detail and are optimising for ideal reaction conditions, catalysts and substrate structure in respect to the sugar derivatives. Therefore, we first developed a quantitative method of analysis for the obtained complex mixtures of reducing sugars which is based on solid phase extraction (SPE), derivatisation and GC-analysis.
With this methodology in hand, we can now evaluate combinations of sugar molecular probes, NHC catalysts and reaction conditions to gain insight into this challenging transformation. In this thorough screening, we were able to determine several key parameters to allow for a fast dehomologation to the desired products but also detected and identified a critical follow-up reactivity. The selectivity between these two main reactions is in the focus of our attention and we discovered first examples with high selectivity for the initially targeted as well as for the observed unexpected transformation, respectively.