Screening study for potential lead compounds for natural product-based fungicides: I. Synthesis and in vitro evaluation of coumarins against Botrytis cinerea

Antifungal Activity and Action Mechanism Study of Coumarins from Cnidium monnieri Fruit and Structurally Related Compounds

The increasing resistance of plant diseases caused by phytopathogenic fungi highlights the need for highly effective and environmentally benign agents. The antifungal activities of Cnidium monnieri fruit extracts and five isolated compounds as well as structurally related coumarins against five plant pathogenic fungi were evaluated. The acetone extract, which contained the highest amount of five coumarins, showed strongest antifungal activity. Among the coumarin compounds, we found that 4-methoxycoumarin exhibited stronger and broader antifungal activity against five phytopathogenic fungi, and was more potent than osthol. Especially, it could significantly inhibit the growth of Rhizoctonia solani mycelium with an EC₅₀ value of 21 μg mL^-1 . Further studies showed that 4-methoxycoumarin affected the structure and function of peroxisomes, inhibited the β-oxidation of fatty acids, decreased the production of ATP and acetyl coenzyme A, and then accumulated ROS by damaging MMP and the mitochondrial function to cause the cell death of R. solani mycelia. 4-Methoxycoumarin presented antifungal efficacy in a concentration- dependent manner in vivo and could be used to prevent the potato black scurf. This study laid the foundation for the future development of 4-methoxycournamin as an alternative and friendly biofungicide.

Bamboo Tar as a Novel Fungicide: Its Chemical Components, Laboratory Evaluation, and Field Efficacy Against False Smut and Sheath Blight of Rice and Powdery Mildew and Fusarium Wilt of Cucumber

The application of agricultural and forest residues can benefit the environment and the economy; however, they also generate a large amount of byproducts. In this study, bamboo tar (BT), a waste product of bamboo charcoal production, was dissolved in natural ethanol and the surfactant alkyl glucoside to manufacture a 50% (wt/wt) BT emulsifiable concentrate (BTEC) biopesticide. BTEC was screened for fungicidal activity against pathogens. The greatest activity was seen against Ustilaginoidea virens with a half-maximal effective concentration (EC₅₀) value of 6 mg/liter. Four phytopathogenic fungi, Podosphaera xanthii, Rhizoctonia solani, Fusarium oxysporum, and Botrytis cinerea, showed EC₅₀ values of <60 mg/liter. Greenhouse tests in vivo showed 2,000 mg/liter BTEC had a 78.4% protective effect against U. virens, and replicated treatments had an 80.6% protective effect. In addition, replicated 2-year field trials were conducted in two geographic locations with four plant diseases: false smut (U. virens), rice sheath blight (Thanatephorus cucumeris [Frank] Donk), cucumber powdery mildew (P. xanthii), and cucumber Fusarium wilt (F. oxysporum). Results showed that 1,000 to 2,000 mg/liter BTEC significantly inhibited these diseases. Gas chromatography-mass spectrometry analysis showed that the total phenolic mass fractions of two BT samples were 45.39 and 48.26%. Eleven components were detected, and their percentage content was as follows (from high to low): 2,6-dimethoxyphenol > 2- or 4-ethylphenol > 2- or 4-methylphenol > phenol > 4-ethylguaiacol > dimethoxyphenol > 4-methylguaiacol > 4-propenyl-2,6-dimethoxyphenol > 2,4-dimethylphenol. Some of the phenolic compounds identified from the tar might be fungicidally active components. BT is a biochar waste, which has potential as a biofungicide and has promise in organic agriculture. The value of this tar may not be because of any fundamental physical differences from other synthetic fungicides but rather caused by reduced production expenses and more efficient use of waste products.

Antifungal Activity against Botrytis cinerea of 2,6-Dimethoxy-4-(phenylimino)cyclohexa-2,5-dienone Derivatives

In this work the enzyme laccase from Trametes versicolor was used to synthetize 2,6-dimethoxy-4-(phenylimino)cyclohexa-2,5-dienone derivatives. Ten products with different substitutions in the aromatic ring were synthetized and characterized using ¹H- and 13C-NMR and mass spectrometry. The 3,5-dichlorinated compound showed highest antifungal activity against the phytopathogen Botrytis cinerea, while the p-methoxylated compound had the lowest activity; however, the antifungal activity of the products was higher than the activity of the substrates of the reactions. Finally, the results suggested that these compounds produced damage in the fungal cell wall.

Pharmacological and Nutritional Effects of Natural Coumarins and Their Structure-Activity Relationships

Coumarins are fused benzene and pyrone ring systems with a wide spectrum of bioactivities, including antitumor, anti-inflammation, antiviral, and antibacterial effects. In this paper, the current development of coumarin-based drugs is introduced, and their structure-activity relationship is discussed by reviewing the relevant literature published in the past 20 years. Coumarin molecules can be customized by the target site to prevent systemic side effects by virtue of structural modification. The ortho-phenolic hydroxyl on the benzene ring has remarkable antioxidant and antitumor activities. Coumarins with aryl groups at the C-4 position have good activities in anti-HIV, antitumor, anti-inflammation, and analgesia. C-3 phenylcoumarins have strong anti-HIV and antioxidant effects. Tetracycline pyranocoumarins can significantly inhibit HIV; osthol structural analogues have antimicrobial activity. Praeruptorin C and its derivatives play an important role in lowering blood pressure and dilating coronary arteries, and khellactone derivatives have significant inhibitory effects on AIDS, cancer, and cardiovascular diseases. It is concluded that the specific site on the core structure of coumarin exhibits one or more activities due to the electronic or steric effects of the substituents. This review is intended to be conducive to rational design and development of more active and less toxic agents with a coumarin scaffold.

6-Methyl-1-(nitromethyl)-4-(propan-2-yl)naphthalene

The title compound, C15H17NO2, was synthesized in two steps from a mixture of α-himachalene (2-methylene-6,6,9-trimethylbicyclo[5.4.01,7]undec-8-ene), β-himachalene (2,6,6,9-tetramethylbicyclo[5.4.01,7]undeca-1,8-diene) and γ-himachalene (2,6,6,9-tetramethylbicyclo[5.4.01,7]undeca-2,8-diene), which was isolated from an essential oil of the Atlas cedar (Cedrus atlantica). The nitro group and the isopropyl group lie almost normal to the mean plane of the naphthalene moiety, making dihedral angles of 83.13 (19) and 71.72 (16)°, respectively, and are inclined to one another by 49.8 (2)°. In the crystal, molecules are linked by pairs of C—H...π interactions and weak C—H...O interactions.

Sterically modulated silver(I) complexes of coumarin substituted benzimidazol-2-ylidenes: Synthesis, crystal structures and evaluation of their antimicrobial and antilung cancer potentials

In this contribution, a series of sterically-encumbered coumarin substituted benzimidazole-based N-heterocyclic carbene (NHC) precursors (1-12) and their silver(I)-NHC complexes (13-24) are reported. Molecular structure of NHC precursors 8 and 12 and cationic complexes 15 and 16 was established by single crystal X-ray diffraction method. The silver(I) complexes demonstrated various significant intramolecular agostic-like interactions operating between the metal center and the hydrogen atoms of the substituents alongside a variety of feeble π-π stacking interactions. A distorted linear coordination geometry is documented at the silver(I) center with the anti-arrangement of the ligands. Further, the complexes demonstrated promising antibacterial properties against Gram positive and Gram negative bacterial strains, especially complex 18 displayed a minimum inhibitory concentration (MIC) of 2 and 4 μg/mL against S. aureus and E. coli, and P. aeruginosa, respectively. Furthermore, complexes 14, 15, 16 and 18 were found cytotoxic against the human lung cancer cell lines A549 and H1975 with the IC₅₀ (concentration of the test sample required to kill 50% of the cell population) value under 10 μM, while mono-NHC complex 20 displayed a potential drug window with the IC₅₀ of 13.7 ± 2.70 and 14.5 ± 1.20 μM against the cancer cell lines H1975 and A549, respectively. Notably, these complexes displayed relatively lesser cytotoxic behaviour against the normal skin fibroblast cell line, Hs68. All the NHC precursors displayed significantly lower biological activities compared with their respective complexes, indicating the utility of silver(I) ions in antimicrobial and antilung cancer applications.

1-(2-Isopropyl-4,7-dimethyl-3-nitronaphthalen-1-yl)ethanone

The title compound, C17H19NO3, was synthesized in four steps from a mixture of α-, β- and γ-himachalene, which was isolated from an essential oil of the Atlas cedar (Cedrus Atlantica). The dihedral angle between the two rings of the naphthalene unit is 1.38 (9)°. The nitro group and the acetyl group lie almost normal to the mean plane of the naphthalene unit, making dihedral angles of 79.35 (16)° and 89.75 (17)°, respectively, and are inclined to one another by 52.9 (2)°. There is an intramolecular C—H...O hydrogen bond present involving a nitro O atom and the H atom of the methyl C atom of the isopropyl group, forming an S(7) ring motif. In the crystal, molecules are linked by pairs of C—H...π interactions, forming inversion dimers. There are no other significant intermolecular interactions present.

6-Bromo-2-(1,4-dibromo-4-methylcyclohexyl)-6-methylheptan-4-one

The title compound, C15H25Br3O, was synthesized in one step from a mixture of α-atlantone [2-methyl-6-(4-methylcyclohex-3-en-1-yl)hepta-2,5-dien-4-one] and γ-atlantone [2-methyl-6-(4-methylcyclohex-3-en-1-ylidene)hept-2-en-4-one], which were isolated from an essential oil of the Atlas cedar (Cedrus Atlantica). The molecule is built up from the bromo ethyl cyclohexane ring, which has a substituent bromomethylhexanone group. The cyclohexane ring adopts a chair conformation. In the crystal, molecules are linked by C—H...O hydrogen bonds, forming zigzag chains parallel to [100].

N-[1,4,4-Trimethyltricyclo[6.3.1.03,9]dodec-8(12)-en-2-yl]acetamide

The title compound, C17H27NO, crystallizes with three independent molecules in the asymmetric unit with almost identical conformations. Each molecule is built up from a seven-membered ring to which a bridged six-membered ring is fused. In each of the three molecules, the seven-membered rings have a twist-chair conformation, while the cyclohexenyl rings display perfect boat conformations. In the crystal, N—H...O hydrogen bonds link the molecules into zigzag chains running along theb-axis direction.

N-[(1aR,5aR,8R,9aR)-1,1-Dichloro-1a,5,5,7-tetramethyl-1a,2,3,4,5,5a,8,9-octahydro-1H-benzo[a]cyclopropa[b][7]annulen-8-yl]acetamide

In the title compound, C18H27Cl2NO, the cyclohexene ring has an envelope conformation, with the C atom at the 9a position as the flap. The cycloheptane ring, to which it is fused, has a boat conformation. The dihedral angle between their mean planes is 60.7 (2)°. The 1,1-dichloro-cyclopropane ring is inclined to these two ring mean planes by 88.5 (3) and 28.3 (3)°, respectively. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming 61helices along thec-axis direction. The absolute configuration of the molecule in the crystal could be fully confirmed from anomalous dispersion effects [Flack parameter = 0.020 (15)].

1-(7-Isopropyl-2,5-dimethyl-8-nitronaphthalen-1-yl)ethanone

The title compound, C17H19NO3, was synthesized in three steps from a mixture of α-, β- and γ-himachalene, which was isolated from an essential oil of the Atlas cedar (Cedrus atlantica). The dihedral angle between the two rings of the naphthalene moiety is 2.54 (5)°. The nitro group and the acetyl group lie almost normal to the mean plane of the naphthalene moiety, making dihedral angles of 80.29 (13) and 83.01 (15)°, respectively, and are inclined to one another by 13.23 (19)°. There is an intramolecular C—H...O hydrogen bond present involving a nitro O atom and the H atom of the methine C atom of the isopropyl group, forming an S(6) ring motif. In the crystal, molecules are linked by pairs of C—H...π interactions, forming inversion dimers. There are no other significant intermolecular interactions present.

(1S,3R,8R)-2,2-Dichloro-3,7,7,10-tetramethyl-11-methylenetricyclo[6.4.0.01,3]dodec-9-ene

The title compound, C17H24Cl2, was synthesized in four steps from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from an essential oil of the Atlas cedar (Cedrus atlantica). The molecule is built from fused six- and seven-membered rings, and an additional three-membered ring. The dihedral angle between the mean planes of the cyclohexene and cycloheptane rings is 58.37 (19)°. There is an intramolecular C—H...Cl hydrogen bond present involving a Cl atom and the H atom of the unique methine C atom, forming an S(5) ring motif. There are no significant intermolecular interactions present.

1-[(1R,2S,4R,7S)-3,3-Dichloro-4,11,11-trimethyltricyclo[5.4.0.02,4]undecan-7-yl]ethanone

The title compound, C16H24Cl2O, crystallizes with two independent molecules in the asymmetric unit. Each molecule is built up from two fused six-membered rings, one of which is fused to a three-membered ring. The two molecules differ essentially in the orientation of two of the methyl groups. The dihedral angles between the mean planes through the two six-membered rings are 57.98 (13) and 55.29 (13)°. The molecular conformation is stabilized by intramolecular C—H...Cl hydrogen bonds.

(1S,2R,8R)-11-Amino-2,2-dichloro-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodec-10-en-9-one

The title compound, C16H23Cl2NO, crystallizes in the monoclinic space groupP21with two independent molecules (AandB) in the asymmetric unit. They have essentially the same conformation. Each molecule is built up from fused six- and seven-membered rings and an additional three-membered ring. The six-membered ring has an envelope conformation, with the C atom belonging to the three-membered ring forming the flap, while the seven-membered ring displays a boat conformation. In the crystal, molecules are linked into chains propagating along thea-axis direction by N—H...O hydrogen bonds.

N-[(3aR*,3bS*)-1,3b,7,7-Tetramethyl-3a,3b,4,5,6,7,7a,7b-octahydro-3H-cyclopenta[3,4]cyclobuta[1,2]benzen-3a-yl]acetamide

The title compound, C17H27NO, is built up from a four-membered ring to which a six- and a five-membered ring are fused. The cyclohexane ring has a chair conformation, while the cyclopentene ring has an envelope conformation, with the C atom substituted by the acetamide group as the flap. The dihedral angles between the mean plane of the central cyclobutane ring and the mean planes of the cyclopentene and cyclohexane rings are 62.52 (2) and 61.06 (11)°, respectively. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming chains propagating along theb-axis direction.

Antifungal activity of umbelliferone derivatives: Synthesis and structure-activity relationships

Umbelliferone was an important allelochemical with a wide spectrum bioactivity. In our previous study, C7 hydroxy in the backbone of umbelliferone was identified to be responsible for its phytotoxicity and the targeted modification of the above site could lead to the phytotoxicity loss. In view of this, a series of hydroxycoumarins and C7 O-substituted umbelliferone derivatives were efficiently synthesized to evaluate their antifungal activity against four phytopathogenic fungi. Most of them, as we predicted, exhibited improved fungicidal activity. The phytotoxicity of effective compounds was also assayed by Lactuca sativa to investigate their side effects on plant growth. Compounds 9 and 17 were identified to show strong antifungal activity with low phytotoxicity. A brief investigation on structure-activity relationships revealed that the modification at the C7 hydroxy of umbelliferone could be a promising way to enhance the antifungal activity with decreasing the phytotoxicity.

Evaluation of antifungal activities and structure-activity relationships of coumarin derivatives

BACKGROUND

Osthol is a natural coumarin and lead compound that has been developed into commercial fungicides in China. Natural coumarins comprise five major subtypes: simple coumarins, linear furanocoumarins, angular furanocoumarins, linear pyranocoumarins and angular pyranocoumarins. Studies pertaining to the antifungal activities of linear pyranocoumarins are few, and no reports exist for the antifungal activities of angular pyranocoumarins. In order to discover more antifungal natural coumarins, we synthesised a series of simple natural coumarins and isolated several plant-based furanocoumarins and pyranocoumarins using previously described methods. The compounds were biologically evaluated against some plant fungal pathogens.

RESULTS

Several of the 35 coumarins evaluated here exhibited strong activities against specific fungal species, including compound 25 (Pd-D-V, a linear pyranocoumarin), compound 26 (libanorin, an angular furanocoumarin) and compound 34 (disenecioyl khellactone, an angular pyranocoumarin). Compound 25 exhibited a high activity against Sclerotinia sclerotiorum (EC₅₀ = 13.2 µg mL^-1 ); compound 34 displayed a strong antifungal activity against Botrytis cinerea (EC₅₀ = 11.0 µg mL^-1 ).

CONCLUSION

This study demonstrates that several natural coumarins (one linear pyranocoumarin and one angular pyranocoumarin in particular) exhibit strong antifungal activities. These results call for further studies, where these coumarins can be examined as potential lead compounds for developing novel antifungal agents. © 2016 Society of Chemical Industry.

1,6-Diacetyl-2-isopropyl-4,7-dimethylnaphthalene

The title compound, C19H22O2, was synthesized in three steps from a mixture of α-, β- and γ-himachalene, which was isolated from an essential oil of the Atlas cedar (Cedrus atlantica). In the crystal, molecules are linked by C—H...O hydrogen bonds into chains running parallel to thebaxis.

N′-[(1S,3R,8R)-2,2-Dichloro-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodecan-11-yl]acetohydrazide

The title compound, C18H26Cl2N2O, was synthesized in four steps from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from an essential oil of the Atlas cedar (Cedrus atlantica). It crystallizes with two independent molecules in the asymmetric unit. Each molecule is built up from fused six- and seven-membered rings and an appended three-membered ring. An acetylhydrazone substituent is attached to the six-membered ring. In both molecules the six-membered rings display half-chair conformations, whereas the seven-membered rings have boat conformations. In the two molecules, the mean planes of the two rings are inclined to one another by 59.9 (3) and 59.1 (3)°. In the crystal, the two molecules are linkedviaN—H...O hydrogen bonds, forming dimers with anR22(8) loop. Within the dimer there are also C—H...O hydrogen bonds present. The dimers are linkedviaC—H...Cl hydrogen bonds, forming slabs parallel to theabplane.

(1S,3R,8R,9S,10R)-2,2-Dichloro-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodecan-9-yl 4-methylbenzene-1-sulfonate

The title compound, C23H31Cl2O3S, was synthesized in three steps from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from essential oil of the Atlas cedar (Cedrus atlantica). The fused six- and seven-membered rings have boat conformations: the dihedral angle between the mean planes of the rings is 88.03 (12)%. The absolute structure was established unambiguously from anomalous dispersion effects. There are no directional interactions in the crystal.

Crystal structure of 1-isopropyl-4,7-dimethyl-3-nitro-naphthalene

The title compound, C15H17NO2, was synthesized from a mixture of α-himachalene (2-methyl-ene-6,6,9-tri-methylbi-cyclo-[5.4.0(1,7)]undec-8-ene) and β-himachalene (2,6,6,9-tetra-methylbi-cyclo-[5.4.0(1,7)]undeca-1,8-diene), which were isolated from an oil of the Atlas cedar (Cedrus Atlantica). The naphthalene ring system makes dihedral angles of 68.6 (2) and 44.3 (2)°, respectively, with its attached isopropyl C/C/C plane and the nitro group. In the crystal, mol-ecules held together by a C-H⋯O inter-action, forming a chain along [-101].

Crystal structure of (1S,3R,8R,9R,10S)-2,4,6-tris-(2,2-di-chloro-3,7,7,10-tetra-methyl-tri-cyclo-[6.4.0.0(1,3)]dodec-9-yl)cyclo-triboroxane

The title compound, C48H75B3Cl6O3, was synthesized in two steps from β-himachalene (3,5,5,9-tetra-methyl-2,4a,5,6,7,8-hexa-hydro-1H-benzo-cyclo-hept-ene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol-ecule consists of an almost planar cyclo-triboroxane ring [maximum deviation = 0.036 (2) Å] linked to three identical fused ring systems with different conformations. Each of the three attached ring systems is built up from a seven-membered ring to which a six- and a three-membered ring are fused. The three six-membered rings have a twist-boat conformation, whereas the seven-membered rings display boat, chair and twist-boat conformations. The dihedral angles between the central boroxane ring and the mean planes of the attached six-membered rings are 63.67 (18), 54.89 (2) and 56.57 (19)°. The crystal packing is governed only by van der Waals inter-actions.

Crystal structure of (1S,3R,8R,9S,10R)-10-bromo-methyl-2,2-di-chloro-9,10-ep-oxy-3,7,7-tri-methyl-tri-cyclo-[6.4.0.0(1,3)]dodeca-ne

The title compound, C₁₆H₂₃BrCl₂O, was synthesized in three steps from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from the essential oil of the Atlas cedar (cedrus atlantica). The mol­ecule is built up from two fused six- and seven-membered rings, each linked to a three-membered ring. The six-membered ring has a screw-boat conformation, whereas the seven-membered ring displays a twist-boat conformation. The absolute structure was established unambiguously from anomalous dispersion effects.

(1S,2R,3S,6S,7R)-3,7,11,11-Tetramethyl-6,7-epoxybicyclo[5.4.0]undecane-2-ol

The title compound, C₁₅H₂₆O₂, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from the Atlas cedar (cedrus atlantica). The mol­ecule is built up from a seven-membered ring to which a six- and a three-membered ring are fused. The seven- and six-membered rings each have a twist-boat conformation. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into zigzag chains running along the b-axis direction.

(1R,4R,6S,7R)-5,5-Di-bromo-1,4,8,8-tetra-methyl-tri-cyclo-[5.4.1.0(4,6)]dodecan-12-one

The title compound, C₁₆H₂₄Br₂O, was synthesized from the reaction of β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from Atlas cedar (Cedrus atlantica). The asymmetric unit contains two independent mol­ecules with similar conformations. Each mol­ecule is built up from two fused seven-membered rings and an additional three-membered ring. In both mol­ecules, one of the seven-membered rings has a chair conformation, whereas the other displays a screw-boat conformation.

1-[(1S,6R,7S,9R)-8,8-Di-bromo-5,5,9-tri-methyl-tri-cyclo-[4.4.0.1(7,9)]decan-1-yl]ethanone

The title compound, C₁₆H₂₄Br₂O, was synthesized by three steps from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from essential oil of the Atlas cedar cedrus atlantica. The asymmetric unit contains two independent mol­ecules with almost identical conformations. Each mol­ecule is built up from two fused six-membered rings, one having a chair conformation and the other a boat conformation, and an additional three-membered ring arising from the reaction of himachalene with di­bromo­carbene. In the crystal, there are no significant intermolecular interactions present. The absolute structure of the title compound was confirmed by resonance scattering.

(1S,3S,8R,10R,11R)-3,7,7,10-Tetramethyltricyclo[6.4.0.01,3]dodecan-11-ol

The title compound, C₁₆H₂₈O, was synthesized by three steps from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus atlantica). The mol­ecule is built up from fused six- and seven-membered rings and an appended three-membered ring. The six-membered ring has twist-boat conformation, whereas the seven-membered ring displays a chair conformation. In the crystal, mol­ecules are linked into chains propagating along the a-axis direction by O—H⋯O hydrogen bonds.

(1S,3R,8R,11S)-11-Bromo-10-bromomethyl-2,2-dichloro-3,7,7-trimethyltricyclo[6.4.0.01,3]dodec-9-ene

The title compound, C₁₆H₂₂Br₂Cl₂, was synthesized from β-him­achalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from fused six- and seven-membered rings and an appended three-membered ring. The six-membered ring has a half-chair conformation, whereas the seven-membered ring displays a chair conformation. The dihedral angle between the two best plane through each ring is 59.5 (2)°. No specific inter­molecular inter­actions were discerned in the crystal packing.

(1S,3R,8R)-2,2-Di-chloro-3,7,7,10-tetra-methyl-tri-cyclo-[6.4.0.0(1,3)]dodec-9-en-11-one

The title compound, C₁₆H₂₂Cl₂O, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzo­cyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from fused six- and seven-membered rings and an additional three-membered ring arising from the reaction of himachalene with di­chloro­carbene. The six-membered ring has an envelope conformation, with the C atom belonging to the three-membered ring forming the flap, whereas the seven-membered ring displays a screw-boat conformation; the dihedral angle between the rings (all atoms) is 59.65 (14)°.

(1S,3R,8R,9R,10S)-2,2-Dibromo-3,7,7,10-tetra-methyl-9β,10β-ep-oxy-3,7,7,10-tetra-methyl-tricyclo-[6.4.0.0(1,3)]dodeca-ne

The title compound, C₁₆H₂₄Br₂O, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus atlantica). The mol­ecule contains fused six- and seven-membered rings, each linked to a three-membered ring. The six-membered ring has a half-chair conformation, while the seven-membered ring displays a chair conformation. The dihedral angle between the mean planes through the six- and seven-membered rings is 39.55 (12)°. The two three-membered rings, linked to the six- and seven-membered rings, are nearly perpendicular to the six-membered ring, making dihedral angles of 78.6 (2) and 80.5 (2)°, respectively. The absolute structure was established unambiguously from anomalous dispersion effects. In the crystal, each mol­ecule is linked to its symmetry-equivalent partner by C—H⋯O hydrogen bonds, forming zigzag chains parallel to [100].

2,2-Dichloro-3,7,7,11-tetra-methyl-10-aza-tetra-cyclo-[6.5.0.0(1,3).0(9,11)]trideca-ne

The title compound, C₁₆H₂₅Cl₂N, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from fused six- and seven-membered rings linked to two three-membered rings. The six-membered ring shows a half-chair conformation, whereas the seven-membered ring displays a boat conformation. The dihedral angle between the mean planes through the six- and seven-membered rings is 59.8 (2)°. The two three-membered rings lie to one side and each is nearly perpendicular to the six-membered ring, forming dihedral angles of 83.2 (2) and 86.0 (2)°. The absolute structure was established unambiguously from anomalous dispersion effects. No specific inter­molecular inter­actions are noted in the crystal structure.

(1S,3R,8R,9S,11R)-2,2,10,10-Tetra-chloro-3,7,7,11-tetra-methyl-tetra-cyclo-[6.5.0.0(1,3).0(9,11)]trideca-ne

The title compound, C(17)H(24)Cl(4), was synthesized from β-himachalene (3,5,5,9-tetra-methyl-2,4a,5,6,7,8-hexa-hydro-1H-benzocyclo-heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol-ecule is built up from fused six- and seven-membered rings and two three-membered rings from the reaction of β-himachalene with dichloro-carbene. The six-membered ring shows a chair conformation, whereas the seven-membered ring displays a boat conformation.

Synthesis, structure-activity relationships (SAR) and in silico studies of coumarin derivatives with antifungal activity

The increased incidence of opportunistic fungal infections, associated with greater resistance to the antifungal drugs currently in use has highlighted the need for new solutions. In this study twenty four coumarin derivatives were screened in vitro for antifungal activity against strains of Aspergillus. Some of the compounds exhibited significant antifungal activity with MICs values ranging between 16 and 32 µg/mL. The structure-activity relationships (SAR) study demonstrated that O-substitutions are essential for antifungal activity. It also showed that the presence of a short aliphatic chain and/or electron withdrawing groups (NO(2) and/or acetate) favor activity. These findings were confirmed using density functional theory (DFT), when calculating the LUMO density. In Principal Component Analysis (PCA), two significant principal components (PCs) explained more than 60% of the total variance. The best Partial Least Squares Regression (PLS) model showed an r2 of 0.86 and q2(cv) of 0.64 corroborating the SAR observations as well as demonstrating a greater probe N1 interaction for active compounds. Descriptors generated by TIP correlogram demonstrated the importance of the molecular shape for antifungal activity.

(1S,3R,8R)-2,2-Dibromo-10-bromomethyl-3,7,7-trimethyltricyclo[6.4.0.01,3]dodec-9-ene

The title compound, C₁₆H₂₃Br₃, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from fused six- and seven-membered rings and an additional three-membered ring from the reaction of himachalene with dibromo­carbene. The six-membered ring has an envelope conformation (the flap atom being the C atom shared with the three-membered ring, whereas the seven-membered ring displays a screw boat conformation; the dihedral angle between the rings (defined by the near coplanar atoms) is 56.5 (2)°.

(1S,3R,8R)-2,2-Dibromo-3,7,7,10-tetra-methyltricyclo-[6.4.0.0(1,3)]dodec-9-en-11-one

The title compound, C₁₆H₂₂Br₂O, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from fused six- and seven-membered rings and an additional three-membered ring from the reaction of himachalene with dibromo­carbene. The six-membered ring has an envelope conformation, with the C atom belonging to the three-membered ring forming the flap, whereas the seven-membered ring displays a screw-boat conformation; the dihedral angle between the rings (all atoms) is 60.92 (16)°.

(1S,3R,8R)-2,2-Dibromo-3,7,7,10-tetra-methyl-tricyclo-[6.4.0.0(1,3)]dodec-9-ene

The title compound, C₁₆H₂₄Br₂, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol­ecule is built up from two fused six- and seven-membered rings and an additional three-membered ring from the reaction of β-himachalene with dibromo­carbene. The six-membered ring shows a screw-boat conformation, whereas the seven-membered ring displays a boat conformation; the dihedral angle between the mean planes through the rings is 57.9 (4)°. The absolute structure was established unambiguously from anomalous dispersion effects.

1-Isopropyl-4,7-dimethyl-2,8-dinitro-naphthalene

The title compound, C₁₅H₁₆N₂O₄, was synthesized from a mixture of α-himachalene (2-methyl­ene-6,6,9-trimethyl­bicyclo­[5.4.O^1,7]undec-8-ene) and β-himachalene (2,6,6,9-tetra­methyl­bicyclo­[5.4.0^1,7]undeca-1,8-diene) which were isolated from an oil of the Atlas cedar (Cedrus atlantica). The asymmetric unit contains two independent mol­ecules. In each of the two mol­ecules, two O atoms of one nitro group are disordered over two sets of sites with site-occupancy factors of 0.636 (5):0.364 (5) and 0.832 (5):0.168 (5). The crystal structure features weak C—H⋯O hydrogen bonds.

Design, synthesis and structure-activity relationship of novel coumarin derivatives

BACKGROUND

The lead coumarin derivative (E)-methyl 3-methoxy-2-[2-(4-methylcoumarin-7-yloxymethyl)phenyl]acrylate was discovered by using an intermediate derivatisation method. To discover new coumarin derivatives with improved activity, a series of substituted coumarins were synthesised and bioassayed.

RESULTS

The compounds were identified by ¹H NMR, IR, MS and elemental analysis. Bioassays demonstrated that some of the title compounds exhibited excellent fungicidal activity against cucumber downy mildew at 25 mg L⁻¹. The relationship between structure and fungicidal activity is reported.

CONCLUSION

The present work demonstrates that coumarin derivatives containing methoxyacrylate moieties can be used as possible lead compounds for developing novel fungicides.

(1S,3R,8R,11S)-2,2-Dichloro-3,7,7,10-tetramethyltricyclo[6.4.0.01,3]dodec-9-en-11-ol

The title compound, C₁₆H₂₄Cl₂O, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from essential oil of the Atlas cedar (Cedrus atlantica). The two fused rings exhibit different conformations: the six-membered ring has a screw-boat conformation, while the seven-membered ring displays a boat conformation. The dihedral angle between the two rings is 56.56 (18)°. In the crystal, mol­ecules aggregate into supra­molecular chains along the c axis mediated by O—H⋯O hydrogen bonds.

(1S,3R,8R)-9-(1-Amino-ethyl-idene)-2,2-dichloro-3,7,7-trimethyl-tricyclo-[6.4.0.0]undecan-10-one

The title compound, C(16)H(23)Cl(2)NO, was synthesised from β-himachalene (3,5,5,9-tetra-methyl-2,4a,5,6,7,8-hexa-hydro-1H-benzocyclo-heptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The mol-ecule contains a seven membered ring, which is fused to a five- and a three-membered ring. The five-membered ring has a twisted conformation, whereas the seven-membered ring displays a chair conformation. The dihedral angle between the five- and seven-membered rings is 45.26 (9)°. The absolute structure was established unambiguously from anomalous dispersion effects. In the crystal, mol-ecules are linked into chains propagating along the b axis by inter-molecular N-H⋯O hydrogen bonds; an intramolecular N-H⋯O link also occurs.

(1S,3R,8S,9R,10S)-2,2-Dichloro-3,7,7,10-tetra-methyl-9,10-ep-oxy-tricyclo-[6.4.0.0]dodeca-ne

The title compound, C₁₆H₂₄Cl₂O, was synthesized from β-himachalene (3,5,5,9-tetra­methyl-2,4a,5,6,7,8-hexa­hydro-1H-benzocyclo­heptene), which was isolated from the essential oil of the Atlas cedar (cedrus atlantica). The mol­ecule forms an extended sheet of two fused rings which exhibit different conformations. The six-membered ring has a half-chair conformation, while the seven-membered ring displays a chair conformation; the dihedral angle between the two rings is 38.2 (1)°.

(1S,2R,8R)-2,2-Dichloro-3,7,7,10-tetra-methyltricyclo-[6.4.0.0]dodec-10-en-9-one

The title compound, C₁₆H₂₂Cl₂O, was synthesized from β-himachalene, which was isolated from essential oil of the Atlas cedar (cedrus atlantica). The asymmetric unit contains two independent mol­ecules, in each of which the six-membered ring shows a half-chair conformation, whereas the seven-membered ring displays a boat conformation. The dihedral angle between the two rings is slightly different in the two mol­ecules [63.22 (13) and 61.81 (14)°].

Forest soil metagenome gene cluster involved in antifungal activity expression in Escherichia coli

Using two forest soils, we previously constructed two fosmid libraries containing 113,700 members in total. The libraries were screened to select active antifungal clones using Saccharomyces cerevisiae as a target fungus. One clone from the Yuseong pine tree rhizosphere soil library, pEAF66, showed S. cerevisiae growth inhibition. Despite an intensive effort, active chemicals were not isolated. DNA sequence analysis and transposon mutagenesis of pEAF66 revealed 39 open reading frames (ORFs) and indicated that eight ORFs, probably in one transcriptional unit, might be directly involved in the expression of antifungal activity in Escherichia coli. The deduced amino acid sequences of eight ORFs were similar to those of the core genes encoding type II family polyketide synthases, such as the acyl carrier protein (ACP), ACP synthases, aminotransferase, and ACP reductase. The gene cluster involved in antifungal activity was similar in organization to the putative antibiotic production locus of Pseudomonas putida KT2440, although we could not select a similar active clone from the KT2440 genomic DNA library in E. coli. ORFs encoding ATP binding cassette transporters and membrane proteins were located at both ends of the antifungal gene cluster. Upstream ORFs encoding an IclR family response regulator and a LysR family response regulator were involved in the positive regulation of antifungal gene expression. Our results suggested the metagenomic approach as an alternative to search for novel antifungal antibiotics from unculturable soil bacteria. This is the first report of an antifungal gene cluster obtained from a soil metagenome using S. cerevisiae as a target fungus.