Synthesis of Tetrahydrobiphenylene via Pd(0)-Catalyzed C(sp2)-H Functionalization.

Tetrahydrobiphenylene consists of cyclobutene fused with benzene and cyclohexene rings. In this paper, a direct method for synthesizing tetrahydrobiphenylenes based on a palladium (Pd)(0)-catalyzed C(sp2)-H functionalization was investigated. The developed method was applied to the synthesis of several tetrahydrobiphenylenes having an oxygen functionality at the ring juncture. The derivatization of a tetrahydrobiphenylene is also reported.

Synthesis and Application of Tetrahydro-2H-fluorenes by a Pd(0)-Catalyzed Benzylic C(sp(3) )-H Functionalization.

A new method has been developed for the synthesis of tetrahydro-2H-fluorenes based on a Pd(0)-catalyzed benzylic C(sp(3) )-H functionalization. Importantly, the success of the cyclization step was dependent on there being substituents at the two positions ortho to the benzylic group to avoid an undesired C(sp(2) )-H functionalization. This method was subsequently used to prepare the right-hand fragment of the hexacyclic triterpenoid benzohopanes, and therefore represents a powerful tool for the construction of the related compounds.

Synthesis of pyrrolophenanthridine alkaloids based on C(sp³)-H and C(sp²)-H functionalization reactions.

Assoanine, pratosine, hippadine, and dehydroanhydrolycorine belong to the pyrrolophenanthridine family of alkaloids, which are isolated from plants of the Amaryllidaceae species. Structurally, these alkaloids are characterized by a tetracyclic skeleton that contains a biaryl moiety and an indole core, and compounds belonging to this class have received considerable interest from researchers in a number of fields because of their biological properties and the challenges associated with their synthesis. Herein, a strategy for the total synthesis of these alkaloids by using C-H activation chemistry is described. The tetracyclic skeleton was constructed in a stepwise manner by C(sp(3))-H functionalization followed by a Catellani reaction, including C(sp(2))-H functionalization. A one-pot reaction involving both C(sp(3))-H and C(sp(2))-H functionalization was also attempted. This newly developed strategy is suitable for the facile preparation of various analogues because it uses simple starting materials and does not require protecting groups.

Design, synthesis, and biological activity of NCC149 derivatives as histone deacetylase 8-selective inhibitors.

We recently discovered N-hydroxy-3-[1-(phenylthio)methyl-1H-1,2,3-triazol-4-yl]benzamide (NCC149) as a potent and selective histone deacetylase 8 (HDAC8) inhibitor from a 151-member triazole compound library using a click chemistry approach. In this work, we present a series of NCC149 derivatives bearing various aromatic linkers that were designed and synthesized as HDAC8-selective inhibitors. A series of in vitro assays were used to evaluate the newly synthesized compounds, four of which showed HDAC8 inhibitory activity similar to that of NCC149, and one of which displayed HDAC8 selectivity superior to that of NCC149. In addition, these top four compounds induced the increase of acetylated cohesin (an HDAC8 substrate) in HeLa cells in a dose-dependent manner, indicating inhibition of HDAC8 in the cells. While none of these compounds enhanced the acetylation of H3K9 (a substrate of HDAC1 and 2), only one compound refrained from increasing α-tubulin acetylation, a substrate of HDAC6, indicating that this compound is more selective for HDAC8 than the other derivatives. Furthermore, this HDAC8-selective inhibitor suppressed the growth of T-cell lymphoma cells more potently than did NCC149. These findings are useful for the further development of HDAC8-selective inhibitors.