Semisynthesis and biological evaluation of ganodermanontriol and its stereoisomeric triols.

The first synthesis of ganodermanontriol, a bioactive lanostane triterpene from the medicinal mushroom Ganoderma lucidum, has been achieved in 15.3% yield over nine steps, along with its three stereoisomeric triols and ganoderol A. The key steps leading to this family of isomers involve the reconstruction of the trisubstituted alkene by stereoselective and chemoselective phosphonate reactions and the formation of the unusual Δ7,9(11)-diene core by the mild acidic opening of a lanosterone-derived epoxide. Ganodermanontriol showed promising activity on the inhibition and proliferation of breast cancer cells. The effect of ganodermanontriol and its isomers on cell proliferation was assayed; IC50 values of 5.8 and 9.7 µM on breast cancer cell lines MCF-7 and MDA-MB-231, respectively, were found for ganodermanontriol.

Olefin metathesis catalysts bearing a pH-responsive NHC ligand: a feasible approach to catalyst separation from RCM products.

Two novel ruthenium-based olefin metathesis catalysts, H(2)ITap(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)ITapCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)ITap = 1,3-bis(2',6'-dimethyl-4'-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene), were synthesized bearing a pH-responsive NHC ligand with two aromatic NMe(2) groups. The crystal structures of complexes and were determined via X-ray crystallography. Both catalysts perform ring opening metathesis polymerization (ROMP) of cyclooctene (COE) at faster rates than their commercially available counterparts H(2)IMes(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)IMesCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)IMes = 1,3-bis(2',4',6'-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) and perform at similar rates during ring closing metathesis (RCM) of diethyldiallylmalonate (DEDAM). Upon addition of 2 equiv. of HCl, catalyst is converted into a mixture of several mono and diprotonated Ru-carbene species 12' which are soluble in methanol but degrade within a few hours at room temperature. Catalyst can be protonated with 2 equiv. of HCl and the resulting complex is moderately water-soluble. The complex is stable in aqueous solution in air for >4 h, but over prolonged periods of time shows degradation in acidic media due to hydrolysis of the NHC-Ru bond. Catalysts and perform RCM of diallylmalonic acid in acidic protic media with only moderate activity at 50 degrees C and do not produce polymer in the ROMP of cationic 7-oxanorbornene derivative under the same conditions. Catalyst was used for Ru-seperation studies when RCM of DEDAM or 3,3-diallypentadione (DAP) was conducted in low-polar organic solution and the Ru-species was subsequently precipitated by addition of strong acid. The Ru-species were removed by (1) filtration and (2) filtration and subsequent extraction with water. The residual Ru-levels could be reduced to as far as 11 ppm (method 2) and 24 ppm (method 1) without the use of chromatography or other scavenging methods.

Reversible inhibition/activation of olefin metathesis: a kinetic investigation of ROMP and RCM reactions with Grubbs' catalyst.

The metathesis activity of Grubbs' catalyst 1 was investigated in the presence of N-donor ligands (1-methylimidazole [MIM], 4-(N,N-dimethylamino)pyridine [DMAP], pyridine, and 1-octylimidazole [OIM]). Ring opening metathesis polymerization (ROMP) reactions of cyclooctene (COE), bulk-ROMP reactions of COE and norbornadiene (NBD), and ring closing metathesis (RCM) reactions of diethyl diallylmalonate (DEDAM) were conducted containing various equivalents of N-donor with respect to catalyst. ROMP reactions could be stopped using MIM (1-5 equiv) and DMAP (2-5 equiv), and slowed with pyridine (1-5 equiv) by factors >100, in benzene solution for 24 h. The stopped reactions could be initiated with excess phosphoric acid (H3PO4), and the reactions proceeded faster than with uninhibited Grubbs' catalyst in the first 4 min after reactivation. Thereafter, the reaction proceeded at the same rate as the reaction with the uninhibited catalyst. ROMP reactions in neat COE and NBD could be inhibited for 72 h using 2 equiv of MIM, DMAP, or OIM and activated with H3PO4 to give polymer gels within minutes or less. RCM reactions could be completely inhibited with MIM (1-5 equiv), but upon treatment with H3PO4, the reaction would proceed at a fraction of the initial rate accomplished by uninhibited Grubbs' catalyst 1. A structural investigation of the inhibited species showed that MIM and DMAP completely or partially transform catalyst 1 into the hexacoordinate species 5a or 5b producing free PCy3, which additionally acts as an inhibitor for the ROMP reaction. Upon reactivation, the PCy3 is protonated along the N-donor ligand; however, over the period of 5 min, the phosphine has been found to coordinate back to the ruthenium catalyst. Therefore, the reaction slows to the same polymerization rate as the reaction using the uninhibited catalyst at this point. Complexes 5a and 5b were isolated, characterized, and employed in ROMP and RCM experiments where they exhibited very low catalytic activity.