Synthesis of Two<scp>d</scp>‐Glucosamine Derived 3,4‐Epoxides as Potential Scaffolds for Combinatorial Chemistry
作者:Lars Svejgaard、Henrik Fuglsang、Peter B. Jensen、Nicholas M. Kelly、Henrik Pedersen、Kim Andersen、Thomas Ruhland、Knud J. Jensen
DOI:10.1081/car-120021699
日期:2003.1.6
Combinatorial chemistry allows the synthesis of libraries of compounds by combination of building blocks or by combinatorial elaboration of a central scaffold.([1,2]) Carbohydrates hold great promise as scaffolds due to their high degree of functionalization, relative conformational rigidity, commercial availability of many stereoisomeric forms, and their well-described chemistry. Hirschmann, Nicolaou, Smith, and their coworkers pioneered the use of carbohydrates as scaffolds in their design and synthesis Of beta-D-glucose derived non-peptide peptidomimetics of the peptide hormone somatostatin (SRIF).([3,4]) However, only relatively few examples on the application of carbohydrates as scaffolds in combinatorial chemistry have been described.([5-11]) For example, Brill et al. anchored a 1,6-anhydro-beta-D-glucopyranoside (levoglucosan) derived epoxide to a solid support and introduced diversity by opening of the support-bound 2,3-epoxide.([9]) Hirschmann et al. employed the opening of a D-glucose derived 1,2-epoxide with a thiol in one of the initial steps towards the synthesis of a library of D-glucose derived compounds. ([10])We reasoned that introduction of all substituents by O-acylation or carbamoylation would give final products with too high a degree of conformational freedom. To introduce substituents directly on the carbohydrate ring and to keep protecting group manipulations on the resin-bound carbohydrate scaffold to a minimum, we decided to prepare a scaffold in which diversity would be introduced by opening of an epoxide. Also, it was a requirement that the scaffold should contain nitrogen, as amines are found in many pharmacologically relevant molecules, e.g., CNS active compounds. We chose inexpensive D-glucosamine as starting material, to prepare a 3,4-epoxide, and to block the C-1 as the methyl glycoside (Scheme 1). Both solution and solid-phase strategies were envisioned; for the solid-phase strategy, the amine could serve as a convenient point for anchoring to a solid support through a Backbone Amide Linker (BAL). ([12,13]) Here we present the synthesis of two new D-glucosamine derived amino epoxides and preliminary studies on opening of one of the epoxides in solution.First, methyl 2-acetamido-2-deoxy-alpha-D-glucopyranoside, 1, easily accessible by Fischer glycosylation, was N-deacetylated by treatment with hydrazine to give known methyl 2-amino-2-deoxy-alpha-D-glucopyranoside 2 (Scheme 1). The N-acetyl group served well here as it was stable to Fischer glycosylation conditions; however, it had to be exchanged with a more labile N-trifluoroacetyl group to allow final deprotection.[GRAPHICS]