Corrected Structure of Natural Hyacinthacine C 1 via Total Synthesis
Hyacinthacines C 1 and C 4 are natural products that were isolated from Hyacinthoides non-scripta and Scilla socialis in 1999 and 2007, respectively. Despite their different 1 H NMR and 13 C NMR spectroscopic data, these compounds have been assigned the same structures, including absolute configurations. This work details the total synthesis of natural (+)-hyacinthacine C 1 , whose structure is confirmed as being the C-6 epimer of that reported. The synthetic strategy focused on inverting the configuration at C-1 of the final hyacinthacines via operating the inversion at the corresponding carbon atom in three previously synthesized intermediates. To do this, the advanced intermediates were subjected to Swern oxidation, followed by a stereoselective reduction with L-Selectride. This approach led to the synthesis of (+)-5-epi-hyacinthacine C 1 (15), the corrected structure for (+)-hyacinthacine C 1 (19), (+)-6,7-di-epi-hyacinthacine C 1 (23), and (+)-7-epi-hyacinthacine C 1 (29). Glycosidase inhibition assays revealed that (+)-hyacinthacine C 1 (19) proved the most active, with IC 50 values of 33.7, 55.5, and 78.2 μM, against the α-glucosidase of rice, human lysosome, and rat intestinal maltase, respectively.