Keng-Yeow Sim

Copper(II) complexes of the antitumour-related ligand salicylaldehyde acetylhydrazone (H2L) and the single-crystal X-ray structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (pyridine) (NO3)}2]

Binary and ternary copper(II) complexes of the ligand salicylaldehyde acetylhydrazone (H2L) have been prepared. In acid or neutral media monoanionic HL complexes separate. Addition of the Lewis bases pyridine (py) and thiourea (tu) to [{Cu(HL)H2O}2] · 2(NO3) results in the monoanionic ternary ligand adducts [{Cu(HL) (py) (NO3)}2] and [Cu(HL) (tu) (NO3)], respectively. With base, the le soluble dianionic complex [{CuL}2] was isolated. Addition of py to [{CuL}2]afforded the dianionic ternary complex [CuL(py)]·12H2O. The complexes have been characterized by a range of physicochemical techniques and the crystal and molecular structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (py) (NO3)}2] determined. Crystals of [{Cu(HL)H2O}2] · 2 (NO3), C18H22Cu2N6O12, are monoclinic, with space group P21/c, a=7.217(4), b=11.758(8), c=13.764(8) A, β=95.47(4)° and Z=4. [{Cu(HL)H2O}2] · 2 (NO3) is a centrosymmetric (planar) dimer, the monomeric units being bridged through the phenoxy oxygen. The copper atom has a square-pyramidal geometry with the basal donor atoms coming from the tridentate ligand (ONO) and the symmetry-related phenolate (O). The more weakly bound apical donor oxygen is supplied by a coordinated water molecule. The nitrate is not bound. Crystals of [{Cu(HL)(py) (NO3)}2], C28H28Cu2N8O10, are monoclinic, with space group P21/c, a=10.642(3), b=11.796(3), c=13.137(2) A, β=111.03(2)° and Z=4. [{Cu(HL) (py) (NO3)}2] is a weakly interacting centrosymmetric (stacked) dimer, the monomeric units being bridged axially through the phenoxy oxygen. The copper atom has a tetragonal geometry with the equatorial donor atoms coming from the tridentate ligand (ONO) and the pyridine (N). The more weakly bound nitrato anion provides the other axial donor (O). Several of the complexes exhibit interesting magnetic properties.

Sampsoniones A–M, a Unique Family of Caged Polyprenylated Benzoylphloroglucinol Derivatives, from Hypericum sampsonii

Abstract Further thorough investigation of the ethanolic extract of the aerial parts of Hypericum sampsonii has yielded sampsoniones K–M which together with the earlier isolated sampsoniones A–J form a unique family of related polyprenylated benzoylphloroglucinol derivatives formed by complex cyclisations of prenyl groups. The structures of these cage compounds have been elucidated by extensive studies of various spectrometric techniques. The 13 metabolites, some of which are bioactive, are probably biosynthesized from a simple common benzoylphloroglucinol precursor.

Versatile chiral palladium(II) complexes for enantiomeric purities of 1,2-diamines

Abstract An efficient NMR determination of the enantiomeric excess of C 2 -symmetric 1,2-diamines can be achieved by coordination of the bidentates to the optically active forms of the diamagnetic [dimethyl(1-(2-naphthyl)ethyl)aminato- C 2 , N ]palladium(II) units.

Triterpenoids, tocotrienols and xanthones from the bark of Cratoxylum Cochinchinense

Abstract A novel bicyclic triterpenoid, polypoda-8(26),13,17,21-tetraen-3β-ol, as well as friedelin, three known tocotrienols, four known xanthones (mangostin, β-mangostin, garcinone D and tovophyllin A) and the previously unreported 2-geranyl-1,3,6-trihydroxy-4-(3,3-dimethylallyl)-xanthone and cratoxylone (1,3,6-trihydroxy-2-(3-hydroxy-3-methylbutyl)-7-methoxy-8-(3,3-dimethylallyl)-xanthone) have been isolated from the bark of Cratoxylum cochinchinense . The structures of the new compounds were determined using a combination of spectroscopic and chemical methods.

A highly stereoselective one-pot asymmetric synthesis of homoallylic amines and amino acids from aldehydes

Abstract A simple and efficient one-pot method was developed to give chiral homoallylic amines and amino acids from the respective aldehydes in high stereoselectivity.

Sampsoniones CH, a unique family of polyprenylated benzophenone derivatives with the novel tetracyclo[7.3.1.13,11.03,7]tetradecane-2,12,14-trione skeleton, from Hypericum sampsonii(Guttiferae)

Abstract The structures of sampsoniones CH, isolated from the aerial parts of Hypericum sampsonii , have been elucidated by extensive analysis of 2 D NMR. Sampsoniones CH are the first polyprenylated benzophenone derivatives with a unique caged tetracyclo[7.3.1.1 3,11 .0 3,7 ]tetradecane-2,12,14-trione skeleton.

Minor xanthones from the bark of cratoxylum cochinchinense

Abstract Three new xanthone derivatives, 11-hydroxy-1-isomangostin, a xanthonolignoid (5′-demethoxycadensin G) and a bisxanthone, as well as the known compound 1,3,5,6-tetrahydroxyxanthone, were isolated from the bark of Cratoxylum cochinchinense. Their structures were elucidated mainly by a combination of high-field NMR spectroscopic techniques.

Novel cytotoxic polyprenylated xanthonoids from Garcinia gaudichaudii (Guttiferae)

Abstract Cytotoxicity guided phytochemical analysis of the leaf extract of the Malaysian medicinal plant Garcinia gaudichaudii led to the isolation of 15 novel cytotoxic compounds, gaudichaudiones A - H ( 1,2,8 – 10 and 12 ), gaudichaudiic acids A - E ( 3 – 6 ), including the known morellic acid ( 7 ) and forbesione ( 11 ). All are mainly tetraprenylated xanthonoids but gaudichaudione H ( 12 ) is a novel bridgehead methoxylated triprenylated xanthonoid. The novel caged structures were determined by detailed NMR spectral analysis and the compounds were found to exhibit significant cytotoxicity against several cancer cell lines.

Complex caged polyisoprenylated benzophenone derivatives, sampsoniones A and B, from Hypericum sampsonii

Abstract The aerial parts of the Chinese medicinal plant Hypericum sampsonii yielded two novel metabolites, sampsoniones A and B, which are characterised by their unique tetracyclo-polyketonic core with benzoyl, 3-methyl-2-butenyl and geranyl substituents. Their structures were determined by detailed spectral analysis. Sampsonione A exhibited moderate cytoxicity to P388 cancer cell line.

Labdane diterpenes from Alpinia zerumbet

Abstract Further studies on the constituents of the seeds of Alpinia zerumbet afforded two new labdane-type diterpenes, zerumin A and zerumin B, together with two known compounds, ( E )-15,16-bisnorlabda-8(17),11-diene-13-one and coronarin E. Their structures were elucidated by spectroscopic techniques.