Antitumor‐Promoting Effects and Cytotoxic Activities of Dammar Resin Triterpenoids and Their Derivatives

Nineteen known triterpenoids, 1 – 19 , and one known sesquiterpenoid, 20 , were isolated from dammar resin obtained from Shorea javanica K. & V. (Dipterocarpaceae). One of the acidic triterpenoids, dammarenolic acid ( 1 ), was converted to fourteen derivatives, namely, an alcohol, 21 , an aldehyde, 22 , and twelve L ‐amino acid conjugates, 23 – 34 . Compounds 1 – 34 were examined for their inhibitory effects on the induction of Epstein–Barr virus early antigen (EBV‐EA) by 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) in Raji cells, a known primary screening test for antitumor promoters. All of the compounds tested, except for compounds 4, 5, 12 – 14, 16 , and 17 , showed inhibitory effects against EBV‐EA activation with potencies either comparable with or stronger than that of β‐carotene, a known natural antitumor promoter. In addition, (20S)‐20‐hydroxy‐3,4‐secodammara‐4(28),24‐dien‐3‐al ( 22 ) exhibited inhibitory effects on skin tumor promotion in an in vivo two‐stage mouse skin carcinogenesis test based on 7,12‐dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as promoter. Furthermore, evaluation of the cytotoxic activities of compounds 1 – 34 against human cancer cell lines showed that reduction (i.e., 21 and 22 ) or conjugation with L ‐amino acids (i.e., 23 – 34 ) of compound 1 enhanced the cytotoxicity against human melanoma cell line CRL1579.     

Synthesis,Characterization, and Anti‐Amoebic Activity of N‐(Pyrimidin‐2‐yl)benzenesulfonamide Derivatives

A new series of N‐(pyrimidin‐2‐yl)benzenesulfonamide derivatives, 3a – 3i and 4a – 4i , was synthesized from pyrimidin‐2‐amines, 2a – 2i , with the aim to explore their effects on in vitro growth of Entamoeba histolytica. The chemical structures of the compounds were elucidated by elemental analysis, FT‐IR, ¹H‐ and ¹³C‐NMR, and ESI mass‐spectral data. In vitro anti‐amoebic activity was evaluated against HM1 : IMSS strain of Entamoeba histolytica. The IC₅₀ values were calculated by using the double dilution method. The results were compared with the IC₅₀ value of the standard drug ‘metronidazole’. The selected compounds were tested for their cytotoxic activities by cell‐viability assay using H9C2 cardiac myoblasts cell line, and the results indicated that all the compounds displayed remarkable >80% viabilities to a concentration of 100 μg/ml.     

Cytotoxic ent‐Kaurane Diterpenoids from Isodon nervosus

Four new ent‐kaurane diterpenoids, rabdonervosins G–J ( 1 – 4 , resp.), were isolated from the leaves and stems of Isodon nervosus. Their structures were elucidated by extensive spectroscopic analyses, including 1D‐, 2D‐NMR and HR mass spectra. Compound 2 showed potent cytotoxicity against the HepG2 and PC‐9/ZD cell lines with IC₅₀ values of 2.36 and 6.07 μM , respectively, and compound 3 exhibited cytotoxicity against the HepG2 and CNE2 cell lines with IC₅₀ values of 8.64 and 9.77 μM , respectively.     

Microbial Reactions on 7α‐Hydroxyfrullanolide and Evaluation of Biotransformed Products for Antibacterial Activity

7α‐Hydroxyfrullanolide ( 1 ), a known sesquiterpenoid, was isolated from Sphaeranthus indicus using an antibacterial‐activity‐directed fractionation method. This compound had exhibited a significant antibacterial activity against Gram‐positive bacteria. Chemical and microbial reactions were performed to prepare eight different analogues of compound 1 in order to evaluate these newly synthesized compounds for antibacterial activity. These compounds were 1β,7α‐dihydroxyfrullanolide ( 2 ), 7α‐hydroxy‐1‐oxofrullanolide ( 3 ), 4,5‐dihydro‐7α‐hydroxyfrullanolide ( 4 ), 11,13‐dihydro‐7α‐hydroxyfrullanolide ( 5 ), 13‐acetyl‐7α‐hydroxyfrullanolide ( 6 ), 2α,7α‐dihydroxysphaerantholide ( 7 ), 4α,5α‐epoxy‐7α‐hydroxyfrullanolide ( 8 ), and 4β,5β‐epoxy‐7α‐hydroxyfrullanolide ( 9 ). Microbial reactions on 1 using whole‐cell cultures of Cunninghamella echinulata and Curvularia lunata yielded compounds 2 – 4 . Incubation of compound 1 with the liquid cultures of Apsergillus niger and Rhizopus circinans yielded metabolites 5 – 7 , while 8 and 9 were prepared by carrying out an epoxidation reaction on 1 using meta‐chloroperbenzoic acid (mCPBA). Structures of compounds 2 – 9 were elucidated with the aid of extensive NMR spectral studies. Compounds 2 – 4 were found to be new metabolites. Compounds 1 – 9 were evaluated for antibacterial activity and found to exhibit a wide range of bioactivities. Antibacterial‐activity data of 1 – 9 suggested that the bioactivity of 1 is largely due to the presence of C(4)?C(5), C(11)?C(13), and a γ‐lactone moiety.     

ent‐Kaurene Diterpenoids from Blepharispermum hirtum

The twigs and leaves of Blepharispermum hirtum Oliver (Asteraceae) were investigated for their larvicidal and antimicrobial activity. Fractionation of the extracts of the twigs, directed by brine shrimp test and antibacterial activities, led to the isolation of compounds 1 – 4 ; two of which are new ent‐kaurene diterpenoids, blepharispins A and B ( 1 and 2 , resp.). The structures of compounds 1 and 2 were established from spectral data. The absolute configuration at C(15) in 1 was inferred from Mosher ester analysis and relative configurations were suggested by a NOESY experiment. Compound 4 was significantly larvicidal to newly hatched naupleii of Artemia salina L. (BST LC₅₀=1.3 (3.7–0.0) μg/ml), but the blepharispins were not (BST LC₅₀>500 μg/ml). Nevertheless, compound 1 inhibited the growth of Staphylococcus aureus and Bacillus subtilis at a MIC value of 62.5 μg/ml. The significance of the bioactivity results and the presence of ent‐kaurene diterpenoids in B. hirtum are discussed from biosynthetic and local utilization viewpoints.     

An Interactive SAR Approach to Discover Novel Hybrid Thieno Probes as Ligands for D2‐Like Receptors with Affinities in the Subnanomolar Range

A series of [(phenylpiperazinyl)alkyl]‐isoindole‐1,3‐dione derivatives was synthesized to serve as probes for dopaminergic receptors. Among this series, compound 6a showed the highest affinity towards D4 and D3 receptors with K_i values in the low nanomolar range, and D2/D4‐ and D2/D3‐selectivity indices of 72 and 20, respectively. Optimization rounds were adopted and led to the D4‐selective ligand thiophene‐2‐carboxamide 9a with a K_i(D4) value of 0.62 nM , and to its butyl analog, 10a , with K_i(D4) and K_i(D3) values of 0.03 and 0.26 nM , respectively. Docking experiments revealed the importance of the unique D4 residue Arg186 in manipulating the ligands' D4‐subtype‐receptor selectivity.     

Biocidal Compounds from Mentha sp. Essential Oils and Their Structure–Activity Relationships

Essential oils from Greek Mentha species showed different chemical compositions for two populations of M. pulegium, characterized by piperitone and pulegone. Mentha spicata essential oil was characterized by endocyclic piperitenone epoxide, piperitone epoxide, and carvone. The bioactivities of these essential oils and their components have been tested against insect pests (Leptinotarsa decemlineata, Spodoptera littoralis and Myzus persicae), root‐knot nematodes (Meloydogine javanica) and plants (Lactuca sativa, Lolium perenne, Solanum lycopersicum). The structure–activity relationships of these compounds have been studied including semi‐synthetic endocyclic trans‐carvone epoxide, exocyclic carvone epoxide, a new exocyclic piperitenone epoxide and trans‐pulegone epoxide. Leptinotarsa decemlineata feeding was affected by piperitenone and piperitone epoxide. Spodoptera littoralis was affected by piperitone epoxide and pulegone. The strongest nematicidal agent was piperitenone epoxide, followed by piperitone epoxide, piperitenone and carvone. Germination of S. lycopersicum and L. perenne was significantly affected by piperitenone epoxide. This compound and carvone epoxide inhibited L. perenne root and leaf growth. Piperitenone epoxide also inhibited the root growth of S. lycopersicum. The presence of a C(1) epoxide resulted in strong antifeedant, nematicidal and phytotoxic compounds regardless of the C(4) substituent. New natural crop protectants could be developed through appropriate structural modifications in the p‐menthane skeleton.     

Development of a highly water-soluble peptide-based human neutrophil elastase inhibitor; AE-3763 for treatment of acute organ injury

A series of peptide-based transition-state human neutrophil elastase (HNE) inhibitors with N-terminal acidic moieties were synthesized and their inhibitory activity against HNE was evaluated both in vitro and in vivo. Our results show that compounds containing cyclic amide bridged acidic moieties at the N-terminal have not only improved water solubility but also high in vivo potency. Among these compounds, AE-3763 showed remarkable efficacy in hamster models of elastase-induced lung hemorrhage and lipopolysaccharide (LPS)-induced lung injury as well as in a mouse model of LPS/galactosamine-induced acute multiple organ dysfunctions. The water solubility of AE-3763 (>1000 mg/ml in H₂O) was also far superior to that of any of the other compounds synthesized. Thus, it is believed that AE-3763 would be useful for treatment of HNE-associated respiratory disorders, such as acute respiratory distress syndrome (ARDS), acute lung injury (ALI), and acute exacerbation of chronic obstructive pulmonary disease (COPD).     

Larvicidal and Structure–Activity Studies of Natural Phenylpropanoids and Their Semisynthetic Derivatives against the Tobacco Armyworm Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)

The larvicidal activity of 18 phenylpropanoids, 1 – 18 , including phenylpropenoate, phenylpropenal, phenylpropene, and their semisynthetic analogues, were evaluated against the tobacco armyworm, Spodoptera litura (Fab .), to identify promising structures with insecticidal activity. Amongst various phenylpropanoids, isosafrole, a phenylpropene, showed the best activity, with an LC₅₀ value of 0.6 μg/leaf cm², followed by its hydrogenated derivative dihydrosafrole (LC₅₀=2.7 μg/leaf cm²). The overall larvicidal activity of various phenylpropene derivatives was observed in the following order: isosafrole ( 6 )>dihydrosafrole ( 16 )>safrole ( 12 )>anethole ( 4 )>methyl eugenol ( 11 )>eugenol ( 13 )>β‐asarone ( 8 )>dihydroasarone ( 18 )>dihydroanethole ( 15 ). Dihydrosafrole might be a promising compound, although presenting a lower larvicidal activity than isosafrole, because of its better stability and resistance to oxidative degradation (due to the removal of the extremely reactive olefinic bond) in comparison to isosafrole. Such structure–activity relationship studies promote the identification of lead structures from natural sources for the development of larvicidal products against S. litura and related insect pests.     

Structure–Activity Relationship Studies on Derivatives of Eudesmanolides from Inula helenium as Toxicants against Aedes aegypti Larvae and Adults

An Aedes aegypti larval toxicity bioassay was performed on compounds representing many classes of natural compounds including polyacetylenes, phytosterols, flavonoids, sesquiterpenoids, and triterpenoids. Among these compounds, two eudesmanolides, alantolactone, and isoalantolactone showed larvicidal activities against Ae. aegypti and, therefore, were chosen for further structure–activity relationship study. In this study, structural modifications were performed on both alantolactone and isoalantolactone in an effort to understand the functional groups necessary for maintaining and/or increasing its activity, and to possibly lead to more effective insect‐control agents. All parent compounds and synthetic modification reaction products were evaluated for their toxic activities against Ae. aegypti larvae and adults. Structure modifications included epoxidations, reductions, catalytic hydrogenations, and Michael additions to the α,β‐unsaturated lactones. None of the synthetic isomers synthesized and screened against Ae. aegypti larvae were more active than isoalantolactone itself which had an LC₅₀ value of 10.0 μg/ml. This was not the case for analogs of alantolactone for which many of the analogs had larvicidal activities ranging from 12.4 to 69.9 μg/ml. In general, activity trends observed from Ae. aegypti larval screening were not consistent with observations from adulticidal screening. The propylamine Michael addition analog of alantolactone was the most active adulticide synthesized with an LC₅₀ value of 1.07 μg/mosquito. In addition, the crystal structures of both alantolactone and isoalantolactone were determined using CuK_α radiation, which allowed their absolute configurations to be determined based on resonant scattering of the light atoms.     

Hypofolins A – L,ent‐Labdane Diterpenoids from the Roots of Hypoestes phyllostachya ‘Pink Splash’

Twelve new ent‐labdane diterpenoids, hypofolins A – F ( 1 – 6 ) and hypofolins G – L ( 7a / 7b , 8a / 8b , and 9a / 9b ), were isolated from the roots of Hypoestes phyllostachya ‘Pink Splash’. Their structures were elucidated by extensive 1D‐ and 2D‐NMR spectroscopic and HR‐MS data. The absolute configurations of 1 , 2 , 5 , and 7a / 7b were determined by single crystal X‐ray diffraction and ECD analysis, as well as chemical transformations. Compounds 7a / 7b , 8a / 8b , and 9a / 9b were isolated as three pairs of interconverting mixture of two isomers between ketone and hemiketal types. Compound 1 showed weak cytotoxicity against SMMC‐7721 cell line with IC₅₀ value of 31.40 μm .     

Influence of (hydroxymethyl)pyridine and pyridine-carboxylic acids, in trans-position to the isopropylamine and amine ligands, on the cytotoxicity of platinum complexes

trans-Pt(II) Complexes with aliphatic amines and planar amines such as (hydroxymethyl)pyridines, and pyridine-3- and pyridine-4-carboxylic acids were synthesized and screened for their potential cytotoxic activity in different cancer cell lines used at the NCI for in vitro screens, i.e., MCF7, NCIH460, and SF268. The complexes studied were designed to differ in geometrical parameters such as the position of the phenyl-group substituents and the nature of the substituents themselves for gathering information about the structure-activity relationships in the trans-complexes. The variation of the substituents turns to be crucial for their biological activity, as both pyridine-3- and pyridine-4-carboxylic acids in trans-position to both amine and isopropylamine ligands provided complexes which displayed no specificity toward any type of cell tested, while (hydroxymethyl)pyridine in trans-position to isopropylamine ligands led to complexes that were clearly more effective against the cell lines tested.     

Synthesis, structure–affinity relationships, and modeling of AMDA analogs at 5-HT2A and H1 receptors: Structural factors contributing to selectivity

Histamine H₁ and serotonin 5-HT_2A receptors present in the CNS have been implicated in various neuropsychiatric disorders. 9-Aminomethyl-9,10-dihydroanthracene (AMDA), a conformationally constrained diarylalkyl amine derivative, has affinity for both of these receptors. A structure–affinity relationship (SAFIR) study was carried out studying the effects of N-methylation, varying the linker chain length and constraint of the aromatic rings on the binding affinities of the compounds with the 5-HT_2A and H₁ receptors. Homology modeling of the 5-HT_2A and H₁ receptors suggests that AMDA and its analogs, the parent of which is a 5-HT_2A antagonist, can bind in a fashion analogous to that of classical H₁ antagonists whose ring systems are oriented toward the fifth and sixth transmembrane helices. The modeled orientation of the ligands are consistent with the reported site-directed mutagenesis data for 5-HT_2A and H₁ receptors and provide a potential explanation for the selectivity of ligands acting at both receptors.     

Synthesis, cytotoxicity, and antitumor activity of lantadene-A congeners

Five new derivatives of the pentacyclic triterpenoid lantadene A (= 22beta-angeloyloxy-3-oxoolean-12-en-28-oic acid; 1) from the leaves of Lantana camara L. were synthesized, characterized, and screened for their cytotoxicities against four human cancer cell lines. The three most-potent compounds, i.e., 1, 4, and 6, with IC50 values in the range of ca. 20-29 microM, were further studied for their in vivo tumor-inhibitory potential upon oral administration in two-stage squamous cell carcinogenesis, using female Swiss albino mice, papilloma being induced by 7,12-dimethylbenz[a]anthracene (DMBA), and promoted by 12-O-tetradecanoylphorbol-13-acetate (TPA). The results are discussed in terms of structure-activity relationship.     

The Loss of a Sugar Chain at C(3) Position Enhances Stemucronatoside K‐Induced Apoptosis,Cell Cycle Arrest,and Hedgehog Pathway Inhibition in HT‐29 Cells

Stemucronatoside K (SMK) and its aglycone stephanthraniline A (STA) are the most representative of a series of novel C₂₁ steriodal compounds that we have previously isolated from Asclepiadaceae plants. The objectives of this study were to investigate the antitumor activity of SMK and STA, and clarify the effect of the sugar chain at the C(3) position. Our results showed that both SMK and STA decreased the growth of HT‐29 cells in a dose‐ and time‐dependent manner. Meanwhile, STA showed much stronger inhibitory effect than SMK. Treatment of HT‐29 cells with STA increased the apoptotic cell numbers and the protein expression of cleaved caspase 3 and cleaved‐PARP. G1 phase cell cycle arrest and decreased expression of cyclin D1 and cyclin‐dependent kinases 4 were also observed after STA treatment. Furthermore, STA reduced the mRNA levels of four Hedgehog pathway components (GLI1, GLI2, GLI3, and PTCH1) and suppressed Shh‐induced Hedgehog pathway activation in a concentration‐dependent manner. These results indicated that SMK and STA could inhibit the growth of HT‐29 cells by inducing apoptosis, cell cycle arrest, and hedgehog pathway inhibition. The loss of sugar chain at C(3) position could enhance SMK's activity. This study is beneficial to understand the use of natural C₂₁ steroids as antitumor lead compounds.