Identification and in vitro anti-esophageal cancer activity of a series of halogenated monoterpenes isolated from the South African seaweeds Plocamium suhrii and Plocamium cornutum

Five known (1, 2, 4, 6 and 7) halogenated monoterpenes together with 1Z,3R^∗,4S^∗,5E,7Z)-1-bromo-3,4,8-trichloro-7-(dichloromethyl)-3-methylocta-1,5,7-triene (3) and (3R^∗,4S^∗)-3,4,6,7-tetrachloro-3,7-dimethyl-octen-1-ene (5) were isolated from the red macroalga Plocamium suhrii and their structures deduced from their spectroscopic data. The seven compounds from P. suhrii together with five related compounds from Plocamium cornutum have been evaluated for their cytotoxic effects on an esophageal cancer cell line (WHCO1). Compounds 1-6 showed greater cytotoxicity in this assay as compared to the known anticancer drug cisplatin.     

New insight in coordination of vic-dioximes: Bis- and tris(E,E-dioximato)Ni(II) complexes

N,N′-Bis[allylamino]glyoxime, N,N′-bis[anilino]glyoxime, and N,N′-bis[1,2,3,4-tetrahydro-5-naphthalenamino]glyoxime have been prepared from corresponding amines and (E,E)-dichloroglyoxime. These ligands gave orange-red compound with NiCl₂ in less acidic medium (pH ∼ 5) that are bis(E,E-dioximato)nickel(II) complexes {[(E,E)-Ni(HL)₂]} (1a-3a) and green compounds in acidic medium (pH ∼ 2) that are tris(E,E-dioximato)nickel(II) dichloride complexes {[(E,E)-Ni(LH₂)₃]Cl₂} (1b-3b). The crystal structures of all complexes have been determined by X-ray diffraction on a single crystal. The study of absorption spectra of these two types of complexes shows that they may be converted to each other by addition of acids (1a-3a) or bases (1b-3b) and there is no way for the amphi form.     

(25S)-Cholesten-26-oic acid derivatives from an Indonesian soft coral Minabea sp.

(25S)-3-Oxocholesta-1,4-dien-26-oic acid (1) and a new (25S)-18-acetoxy-3-oxocholesta-1,4-dien-26-oic acid (2) were isolated from a soft coral Minabea sp. (cf. aldersladei) collected in North Sulawesi, Indonesia, together with two known cholic-acid-type compounds, 3-oxochol-1,4-dien-24-oic acid (3) and 3-oxochol-4-en-24-oic acid (4). The structures of these compounds were determined on the basis of their spectroscopic data. The absolute stereochemistry at C-25 of 2 was determined by comparative ¹H NMR study using chiral anisotropic reagents [(S)- and (R)-phenylglycine methyl esters]. This is the first to report compound 1 as a natural product.     

New triterpenoid saponins from the roots of Gypsophila pacifica Kom.

Six new triterpenoid saponins (1-6) have been isolated from the roots of Gypsophila pacifica Kom. Their structures were established on the basis of extensive NMR (¹H, ¹³C, TOCSY, HSQC, and HMBC) and ESIMS studies.     

Antitumoral and antileishmanial dioncoquinones and ancistroquinones from cell cultures of Triphyophyllum peltatum (Dioncophyllaceae) and Ancistrocladus abbreviatus (Ancistrocladaceae)

From the methanolic extracts of solid callus cultures from two species of the closely related palaeotropical plant families Dioncophyllaceae and Ancistrocladaceae seven new natural naphthoquinones were isolated, dioncoquinones A (4) and B (5) from Triphyophyllum peltatum, and ancistroquinones B (6), C (7), D (9), E (10), and F (12) from Ancistrocladus abbreviatus. Their structures were elucidated by spectroscopic, chemical, and computational methods. Furthermore, the already known naphthoquinones plumbagin (2), droserone (3), malvone A (8), and nepenthone A (11) were found in the extract of A. abbreviatus. Dioncoquinones A (4) and B (5) showed good - and specific - activity against Leishmania major, while they were not active against other protozoic parasites. Moreover, treatment with 4 and 5 strongly induced apoptosis in human tumor cells derived from two different B cell malignancies, B cell lymphoma and multiple myeloma, without any significant toxicity towards normal peripheral mononuclear blood cells.     

Exploring the effect of chain length of bridging ligands in coordination complexes and polymers derived from mixed ligand systems of pyridylnicotinamides and dicarboxylates

The supramolecular structural diversities in mixed ligand systems derived from a series of dicarboxylate anions with varying chain lengths and N-donor exo-bidentate ligand equipped with hydrogen bonding capable amide backbone with Co(II)/Zn(II) metal centers are analyzed. In this context, two complexes namely (Co(L1)₂(malonate)(H₂O)₂} (1a), {Zn(L1)₂(malonate)(H₂O)₂} (1b) and one coordination polymer namely {[Co(μ-L1)(μ-glutarate)(H₂O)] · H₂O}_n (4) (where L1 = N-(4-pyridyl)nicotinamide) have been synthesized and crystallographically characterized. The main aim of this work is to explore the effects of chain lengths of the anionic carboxylate ligands such as malonate, succinate, maleate, and glutarate, in determining the final architecture of coordination compounds based on the mixed ligands. Analyses of the structures revealed that the length of the bridging ligands have prominent effect in the formation of hierarchical structures.     

Concomitant polymorphism: Crystallising dichloro-bis(2,4-lutidine)-zinc as both chiral and racemic phases

The crystallisation of dichloro-bis(2,4-lutidine)-zinc from various solvents (e.g. ethanol, THF and 2,4-lutidine) has been investigated and two phases were isolated. The structures of both phases were determined by single crystal X-ray diffraction and both types of crystals were found to be composed of conformationally chiral molecules. One phase (α-1) is racemic and crystallises in space group P2₁/c, while the other phase (β-1) crystallises in the enantiomorphous space group P4₁2₁2 with a low Flack parameter. In a few cases the chiral and racemic phases crystallised concomitantly; this phenomenon is rare and can be useful in the development of tools for the prediction of crystal structures.     

Isolation and structural studies on the alkaloids of Petchia ceylanica

(19R)-Epimisiline and (19S)-epimisiline, two new Aspidosperma alkaloids, have been isolated from the leaves of Petchia ceylanica. The structures have been deduced on the basis of chemical and spectroscopic data.     

Two piperazic acid-containing cyclic hexapeptides from Streptomyces alboflavus 313

Two novel cyclic hexapeptides, designated NW-G10 (1) and NW-G11 (2), were isolated from the fermentation broth of Streptomyces alboflavus 313. Their relative structures were elucidated on the basis of extensive spectroscopic analysis, and the absolute configurations of several constituent amino acids were determined by Marfey’s method. NW-G10 (1) and NW-G11 (2) exhibited significant activity against Gram-positive bacteria, such as Bacillus cereus, Bacillus subtilis and Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus (MRSA), but they are not active against gram negatives.     

Two novel hydroperoxylated products of 20(S)-protopanaxadiol produced by Mucor racemosus and their cytotoxic activities against human prostate cancer cells

Microbial transformation of 20(S)-protopanaxadiol (1) by Mucor racemosus AS 3.205 yielded two novel hydroperoxylated metabolites and three known hydroxylated metabolites. The structures of the metabolites were identified as 26-hydroxyl-20(S)-protopanaxadiol (2), 23,24-en-25-hydroxyl-20(S)-protopanaxadiol (3), 25,26-en-24(R)-hydroperoxyl-20(S)-protopanaxadiol (4), 23,24-en-25-hydroperoxyl-20(S)-protopanaxadiol (5), and 25-hydroxyl-20(S)-protopanaxadiol (6). 4 and 5 are new compounds. Metabolites 2, 4, and 5 showed the more potent inhibitory effects against DU-145 and PC-3 cell lines than the substrate.     

1-Methylisocytosine as a ligand for (dien)M (M = Pt, Pd) and Pt-promoted deamination to 1-methyluracil

1-Methylisocytosine (1-MeIC) can be protonated at the endocyclic N(3) position (pK_a of 1-MeICH⁺, 4.02 ± 0.04) or complexed at this position with (dien)M^II (M = Pt, Pd). X-ray crystal structures of the protonated species 1 as well as the Pd (2) and Pt (3) complexes are reported, and gas phase structures of the cation 2 and 3 have been calculated by ab initio methods. These results are compared with results from X-ray crystallography. At high pH, the Pt complex 3 undergoes deamination of the exocyclic N(2)H₂ group to the 1-methyluracilate complex. As compared to the situation with 1-methylcytosine (1-MeC), the accelerating effect of (dien)Pt^II is much less pronounced, however.     

Bridged dinucleating N-heterocyclic carbene ligands and their double helical mercury(II) complexes

A series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H₂L]Cl₂ (1a)-(6a) and [H₂L](PF₆)₂ (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-C²H units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg₂L₂](PF₆)₄ (7)-(9) are readily formed in good yields from ligand precursors [H₂L](PF₆)₂ and Hg(OAc)₂, as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg₂L₂]⁴⁺ cations. Ligand scrambling in [Hg₂L₂]⁴⁺ occurs only in the presence of free carbene precursor, presumably via an associative mechanism.     

Intramolecular ether oxygen coordination in the zinc complexes with dipicolylamine (DPA)-derived ligands

The ether oxygen coordination to the zinc center in the complexes with dipicolylamine (DPA)-derived ligands, N-(2-methoxyethyl)-N,N-bis(2-pyridylmethyl)amine (L), N-(3-methoxypropyl)-N,N-bis(2-pyridylmethyl)amine (L′), and N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-pyridylmethyl)amine (L^Py) has been discussed. Upon chelation of the oxygen atom, L forms a five-membered chelate ring with respect to the 2-aminoethyl ether moiety whereas L′ forms a six-membered chelate in 3-aminopropyl ether unit. This difference was highlighted by the crystal structures of ZnCl₂ complexes, in which [Zn(L)Cl₂] (1) exhibited ether oxygen coordination but [Zn(L′)Cl₂] (2) had the ether oxygen non-coordinated. The terminal pyridyl group of L^Py facilitates the ether oxygen atom coordination via a metal binding from the basal plane trans to the aliphatic nitrogen.     

Antibacterial clerodane diterpenes from Goldenrod (Solidago virgaurea)

Nine clerodane diterpenes, solidagoic acids C-I (1-7), cleroda-3,13(14)-dien-16,15:18,19-diolide (8) and cleroda-3,13(14)-dien-15,16:18,19-diolide (9) were isolated and characterised from the ethanol-ethyl acetate (1:1) extract of Solidago virgaurea. The structures were determined by NMR spectroscopic analysis. Several displayed moderate antibacterial activity against Staphylococcus aureus.     

Aporphine alkaloids and cytotoxic lignans from the roots of Illigera luzonensis

Six aporphine alkaloids, (+)-(S)-N-butyrylcaaverine (1), (+)-(S)-N-propionylcaaverine (2), (+)-(S)-N-acetylcaaverine (3), (+)-(6aR,7R)-N-butyrylnorushinsunine (4), (+)-(6aR,7R,E)-N-(but-2-enoyl)norushinsunine (5), and N-formyldehydrocaaverine (6) were isolated from the roots of Illigera luzonensis, together with 16 known compounds. Their structures were determined through spectroscopic and MS analyses. Among the isolates, (−)-deoxypodophyllotoxin (13) was the most cytotoxic, with IC₅₀ values of 0.0057, 0.0067, 0.00004, and 0.0035 μg/mL, respectively, against DLD-1, CCRF-CEM, HL-60, and IMR-32 cell lines. In addition, (−)-yatein (12) exhibited cytotoxic effects, with IC₅₀ values of 0.81, 0.20, and 0.59 μg/mL, respectively, against DLD-1, CCRF-CEM, and HL-60 cell lines.     

New four- and five-coordinated complexes of cobalt with sterically hindered o-iminobenzoquinone ligands: synthesis and structure

New square planar Co^II(ISQ-iPr)₂ (1), Co^II(ISQ-Me)₂ (2) and five-coordinate Co^III(ISQ-Me)₂Cl cobalt complexes (3) (ISQ-iPr=4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate radical-anion, ISQ-Me=4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate radical-anion) have been prepared using different methods. Complexes 1-3 have been characterized by IR, UV-Vis, EPR spectroscopy. Molecular structures of 1 and 3 were determined using X-ray crystallography. It has been established from variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy that 1 and 2 possess an S=1/2 ground state. In the complex molecules the unpaired electrons of o-iminobenzosemiquinonate radical ligands (S_rad=1/2) are strongly coupled antiferromagnetically. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands prevent the formation of a hexacoordinate species.     

Indanone and mellein derivatives from the Garcinia-derived fungus Xylaria sp. PSU-G12

Two new compounds, one indanone (1) and one mellein (2), along with 3-hydroxy-4-methyl-1-indanone (3), griseofulvin (4), dechlorogriseofulvin (5), cytochalasin D (6) and three mellein derivatives (7–9) were isolated from the broth extract of the Garcinia-derived fungus Xylaria sp. PSU-G12. The structures were elucidated by spectroscopic analysis. This is the first report on the isolation of indanone derivatives from the genus Xylaria. The isolated compounds were evaluated for antioxidant activity in DPPH assay.     

Toxic polyketides produced by Fusarium sp., an endophytic fungus isolated from Melia azedarach

A new isocoumarin derivative named fusariumin (1), together with two known related resorcylic acid lactones aigialomycin D (2) and pochonin N (3), has been isolated from the cultures of Fusarium sp. LN-10, an endophytic fungus originated from the leaves of Melia azedarach. Their structures were established on the basis of extensive spectroscopic analyzes including 1D- and 2D- NMR (¹H-¹H COSY, HSQC, HMBC, and NOESY) experiments. Compounds 1-3 displayed significant growth inhibitory activity against the brine shrimp (Artemia salina).     

Steroids from the leaves of Chinese Melia azedarach and their cytotoxic effects on human cancer cell lines

Three new (1-3) and several known (4-6) steroids were isolated from the leaves of Chinese Melia azedarach. The structures of the new compounds were elucidated by means of spectroscopic methods including 2D NMR techniques and mass spectrometry to be (20S)-5,24(28)-ergostadiene-3β,7α,16β,20-tetrol (1), (20S)-5-ergostene-3β,7α,16β,20-tetrol (2), and 2α,3β-dihydro-5-pregnen-16-one (3). The cytotoxicities of the isolated compounds against three human cancer cell lines (A549, H460, U251) were evaluated; only compounds 1, 2, and (20S)-5-stigmastene-3β,7α,20-triol (4) were found to show significant cyctotoxic effects with IC₅₀s from 12.0 to 30.1 μg/mL.