A compound isolated from Alpinia officinarum Hance. inhibits swarming motility of Pseudomonas aeruginosa and down regulates virulence genes

AIM

The study was aimed at purifying the active principle from Alpinia officinarum rhizomes responsible for inhibition of swarming motility of Pseudomonas aeruginosa and analysing the mechanism of action.

METHODS AND RESULTS

The active compound from methanol extract of A. officinarum was purified by silica gel column chromatography followed by elution from Amberlite resin. The compound 1-(3,5-dihydroxyphenyl)-2-(methylamino)ethan-1-one, inhibited swarming motility at 12·5 µg ml^-1 . This inhibition was independent of rhamnolipid production. Real-time PCR analysis showed significant down-regulation of virulence-associated genes including T3SS exoS, exoT and flagella master regulator fleQ.

CONCLUSIONS

The compound from A. officinarum inhibited swarming motility and significantly down-regulated the expression of type III secretory system effector genes exoS and exoT and flagellar master regulator fleQ genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study identifies a potent swarming inhibitory compound from the common medicinal plant A. officinarum and reinstates the potential of plant-derived compounds in tackling virulence properties of pathogenic bacteria.

Methyl (E)-2-cyano-3-(6-nitro-1,3-benzodioxol-5-yl)acrylate

In the title compound, C₁₂H₈N₂O₆, the 1,3-benzodioxole ring system is essentially planar [maximum deviation = 0.036 (2) Å] and the nitro group is oriented at a dihedral angle of 15.4 (1)° with respect to its mean plane. In the crystal, moleucles are linked into C(8) [101] chains by C—H⋯O hydrogen bonds, and weak aromatic π–π stacking [centroid–centroid distance = 3.887 (1) Å] also occurs.

(E)-Methyl 2-[(1,3-dioxoisoindolin-2-yl)methyl]-3-phenylacrylate

In the title compound, C₁₉H₁₅NO₄, the isoindole ring system is essentially planar [maximum deviation = 0.011 (1) Å] and is oriented at a dihedral angle of 75.7 (1)° with respect to the phenyl ring. The mol­ecular conformation is stabilized by an intra­molecular C—H⋯O hydrogen bond. The crystal packing is stabilized by C—H⋯O hydrogen bonds, which generate zigzag chains along the a axis. The crystal packing is further stabilized by a C—H⋯π inter­action.

(Z)-3-(2-Meth-oxy-benz-yl)-1,5-benzo-thia-zepin-4(5H)-one

In the title compound, C₁₇H₁₅NO₂S, the seven-membered thia­zepine ring adopts a distorted twist-boat conformation. The dihedral angle between the mean planes of the benzothia­zepin ring system and the attached benzene ring is 47.7 (1)°. In the crystal, pairs of N—H⋯O hydrogen bonds link inversion-related mol­ecules into dimers, generating R₂²(8) ring motifs. These dimers are further connected into a chain along the a axis by C—H⋯O hydrogen bonds, resulting in R₂²(14) ring motifs. The crystal packing also features C—H⋯π inter­actions.

(Z)-3-(4-Chloro-benz-yl)-1,5-benzothia-zepin-4(5H)-one

In the title compound, C(16)H(12)ClNOS, the seven-membered thia-zepine ring adopts a distorted twisted boat conformation. The dihedral angle between the least-squares planes of the 1,5-benzothia-zepine ring system and the benzene ring is 50.2 (1)°. In the crystal, pairs of N-H⋯O hydrogen bonds link centrosymmetrically related mol-ecules into dimers, generating R(2) (2)(8) ring motifs. The crystal packing is further stabilized by π-π inter-actions [centroid-centroid distance = 3.763 (2) Å].

Methyl (2E)-2-({2-[(2E)-2-benzylidene-3-methoxy-3-oxopropyl]-1,3-dioxoindan-2-yl}methyl)-3-phenylprop-2-enoate

In the title compound, C₃₁H₂₆O₆, the five-membered ring of the indane unit adopts a slight envelope conformation with the flap atom displaced by 1.38 (14) Å. The mol­ecular conformation is stabilized by an intra­molecular C—H⋯O hydrogen bond, which generates an S(9) ring motif. In the crystal, pairs of C—H⋯O hydrogen bonds link centrosymmetrically related mol­ecules into dimers, generating R₂²(22) ring motifs. The crystal packing is further stabilized by C—H⋯π inter­actions.

(E)-Methyl 3-(3,4-dimeth-oxy-phen-yl)-2-[(1,3-dioxoisoindolin-2-yl)meth-yl]acrylate

In the title compound, C(21)H(19)NO(6), the isoindole ring system is essentially planar [maximum deviation = 0.019 (2) Å for the N atom] and is oriented at a dihedral angle of 51.3 (1)° with respect to the benzene ring. The two meth-oxy groups are almost coplanar with the attached benzene ring [C-O-C-C = 3.7 (4) and 4.3 (4)°]. The mol-ecular conformation is stabilized by an intra-molecular C-H⋯O hydrogen bond, which generates an S(9) ring motif. In the crystal, mol-ecules are linked through bifurcated C-H⋯(O,O) hydrogen bonds having R(1) (2)(5) ring motifs, forming chains along the b-axis direction. The crystal packing is further stabilzed by π-π inter-actions [centriod-centroid distance = 3.463 (1) Å].

2-(2H-1,3-Benzodioxol-5-yl)-1,3-benzothiazole

In the title compound, C₁₄H₉O₂S, the benzothia­zole unit is oriented at a dihedral angle of 7.1 (1)° with respect to the benzodioxole unit. The dioxole ring adopts flattened envelope conformation with the methyl­ene C atom at the flap. The crystal packing is stabilized by π–π inter­actions [centroid–centroid distances = 3.705 (1) and 3.752 (1) Å], C—H⋯π inter­actions and a short S⋯S contact of 3.485 (1) Å.

1'-Methyl-4'-(4-methyl-phen-yl)dispiro-[1-benzopyran-3(4H),3'-pyrrolidine-2',3''-indoline]-2,2''-dione

In the title compound, C₂₇H₂₄N₂O₃, the pyrroldine ring adopts a twist conformation, while the six-membered pyran­one ring of the coumarin ring system is in a sofa conformation. In the crystal, pairs of N—H⋯O hydrogen bonds link the mol­ecules into inversion R₂²(8) dimers. These dimers are further connected via C—H⋯O hydrogen bonds.

1',6-Dimethyl-4'-phenyl-dispiro-[1-benzopyran-3(4H),3'-pyrrolidine-2',3''-indoline]-2,2''-dione

In the title compound, C₂₇H₂₄N₂O₃, the five-membered pyrroldine ring adopts an envelope conformation (with the N atom in the flap position) and the six-membered pyran­one ring of the coumarine ring system adopts a slightly distorted boat conformation. The oxindole unit makes dihedral angles of 89.7 (1) and 25.6 (1)°, respectively, with the pyrrolidine ring and the coumarin ring system. The mol­ecular structure is stabilized by two intra­molecular C—H⋯O contacts and two intra­molecular π–π inter­actions [centroid–centroid seperations of 3.514 (1) and 3.623 (1) Å]. The crystal packing features N—H⋯O hydrogen bonds, which link the mol­ecules into cyclic centrosymmetric R₂²(8) dimers, and C—H⋯π inter­actions.

(E)-N-(Anthracen-9-ylmethylidene)-4-nitroaniline

In the title molecule, C₂₁H₁₄N₂O₂, the anthracenyl system is approximately planar [maximum deviation = 0.056 (4) Å] and is oriented at a dihedral angle of 73.6 (1)° with respect to the benzene ring. An intra­molecular C—H⋯N hydrogen bond generates an S(6) ring motif. The crystal packing is stabilized by C—H⋯π and π–π inter­actions [centroid–centroid distances of 3.688 (2), 3.656 (1) and 3.716 (2) Å].

2-(1,3-Benzothia-zol-2-yl)-6-eth-oxy-phenol

In the title compound, C(15)H(13)NO(2)S, the benzothia-zole unit is essentially planar [maximum deviation = -0.0099 (5) Å for the S atom] and is oriented at a dihedral angle of 4.8 (5)° with respect to the benzene ring. An intra-molecular O-H⋯N hydrogen bond generates an S(6) ring motif. The crystal packing is stabilized by C-H⋯π inter-actions.