The posttranslational modification of neural cell-adhesion molecule (NCAM) with polysialic acid (PSA) and the spatiotemporal distribution of PSA-NCAM play an important role in the neuronal development. In this work, we developed a tissue-based strategy for metabolically incorporating an unnatural monosaccharide, peracetylated N-azidoacetyl-D-mannosamine, in the sialic acid biochemical pathway to present N-azidoacetyl sialic acid to PSA-NCAM. Although significant neurotoxicity was observed in the conventional metabolic labeling that used the dissociated neuron cells, neurotoxicity disappeared in this modified strategy, allowing for investigation of the temporal and spatial distributions of PSA in the primary hippocampal neurons. PSA-NCAM was synthesized and recycled continuously during neuronal development, and the two-color labeling showed that newly synthesized PSANCAMs were transported and inserted mainly to the growing neurites and not significantly to the cell body. This report suggests a reliable and cytocompatible method for in vitro analysis of glycans complementary to the conventional cell-based metabolic labeling for chemical glycobiology.

A facile total synthesis of the reported structure for panaginsene through a trimethylenemethane (TMM) diyl mediated tandem cycloaddition reaction revealed that the spectroscopic data of the synthesized structure did not match with the data of the natural product. The total synthesis of the stereoisomer of the reported structure confirmed that the correct structure of panaginsene was the 11-epi stereoisomer of the originally proposed structure of panaginsene.

The first total synthesis of (±)-jujuyane, a cyclooctanoid natural product, was accomplished from a (5 + 3) dimerization product of oxidopyrylium ylide that forms the cyclooctanoid core structure along with inherited stereochemical bias. Selective functional group modifications of the highly oxygenated dimeric structure, followed by the tactical functional group manipulation around the eight-membered carbocyclic core, enabled the total synthesis of (±)-jujuyane, which will serve a guide for future applications of oxidopyrylium dimers to the natural product total synthesis.

Total Synthesis of Panaginsene with Structural Revision. -In order to confirm the proposed structure of the tricyclic sesquiterpene panaginsene (I), which is isolated from the roots of Panax ginseng, the total synthesis of (I) and its epimer (II) is described. Compound (I) is synthesized from (R)-citronellal by a tandem cycloaddition and racemic (II) from 2-methyl-1,3-propanediol. NOE-experiments reveal that compound (II) is the correct structure of panaginsene. -(GEUM, S.; LEE*, H.-Y.; Org. Lett. 16 (2014) 9, 2466-2469, http://dx.doi.org/10.1021/ol500849m ; Dep. Chem., Korea Adv.