Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands for Main Group Elements.

The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe3 and 2-EMe3 (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N3 EMe3 -derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe3 yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe3 )2 (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO2 yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C5 Me5 ), BBr2 Ar (Ar=Ph, Mes, 2-thienyl), ECl3 (E=B, Al, Ga) and PX3 (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr3 resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution 11 B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C4 BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic 11 B NMR resonances is linearly correlated to both the degree of twisting of the C4 BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent.

Lanostane-type triterpenoids from Ganoderma applanatum and their inhibitory activities on NO production in LPS-induced BV-2 cells.

Five previously undescribed lanostane-type triterpenoids, including two triterpenoids with a rearranged side chain (applanoic acids E and F), one C21 nortriterpenoid (16,17-dehydroapplanone E), as well as two highly oxygenated lanostane triterpenoids (methyl applaniate B and applanoic acid G), were isolated from the fruiting bodies of Ganoderma applanatum (Pers.) Pat. Their structures were elucidated on the basis of spectroscopic analysis, X-ray crystallography and ECD data. Applanoic acid E, 16,17-dehydroapplanone E, and methyl applaniate B showed inhibitory effects on the release of NO by LPS-induced BV-2 cells.

Lanostane-type triterpenoids from the fruiting bodies of Ganoderma applanatum.

Twelve previously undescribed lanostane-type triterpenoids, including three triterpenoids with a γ-lactone ring, namely applanlactones A‒C, four highly oxygenated lanostane triterpenoids, namely methyl applaniate A and applanoic acids B‒D, as well as five C21 nortriterpenoids, applanones A‒E were isolated from the fruiting bodies of Ganoderma applanatum (Pers.) Pat.. Their structures were elucidated by 1D, 2D NMR and MS spectra, as well as X-ray crystallographic analyses. Meanwhile, applanlactone A, methyl applaniate A and applanoic acid B showed inhibitory effects for the proliferation of hepatic stellate cells (HSCs) induced by transforming growth factor-ß1 (TGF-ß1) in vitro.

X-ray crystal structure guided discovery of new selective, substrate-mimicking sirtuin 2 inhibitors that exhibit activities against non-small cell lung cancer cells.

Human sirtuin 2 (SIRT2) is a nicotinamide adenine dinucleotide (NAD+)-dependent deacylase, and is implicated in human diseases including cancer. Selective small-molecule inhibitors for SIRT2 are sought as chemical tools and potential therapeutics. Here we report the X-ray crystal structure guided structure-activity relationship studies of new N-(3-(phenoxymethyl)phenyl)acetamide derivatives with SIRT2, which led to the identification of potent, selective SIRT2 inhibitors. Crystallographic analyses reveal that the new inhibitors act via inducing the formation of an enlarged hydrophobic pocket and particularly mimicking the interactions made by myristoylated-lysine substrates. The most potent inhibitor 24a could dose-dependently elevate the acetylation level of α-tubulin in the non-small cell lung cancer H441 cells, which have a high expression level of SIRT2 as determinated by Western blotting analyses. Further cellular assays reveal that 24a restrains cell growth mainly through inhibiting cellular proliferation rather than inducing apoptosis. Moreover, 24a could suppress the migration and invasion of H441 cells. These results provide an excellent basis for further development of new potent, selective, and cell active SIRT2 inhibitors as chemical tools and potential therapeutics for SIRT2-driven non-small cell lung cancers.

Two new bufadienolides from the rhizomes of Helleborus thibetanus with inhibitory activities against prostate cancer cells.

Two new bufadienolide glycosides (1 and 2) with an A/B trans ring fusion together with nine known compounds (3-11) were isolated from the rhizomes of Helleborus thibetanus. The structures of new compounds were elucidated by extensive spectroscopic analyses in combination with single-crystal X-ray diffraction. The bufadienolides 1 and 3-6 exhibited potent cytotoxic activities against the prostate cancer cells.