Synthesis and inhibitory potential towards acetylcholinesterase, butyrylcholinesterase and lipoxygenase of some variably substituted chalcones

A series of variably substituted chalcones were synthesized by condensation of substituted acetophenones with mono-, di- or trisubstituded benzaldehydes. It was observed that some of these compounds have the potential to inhibit acetylcholinesterase, whereas others show activity against butyrylcholinesterase, depending on the substitution pattern at the two aromatic rings of these chalcones. Similarly, lipoxygenase was inhibited by two of these compounds. It has been observed that inhibition of the three enzymes was concentration dependent with the IC50 values ranging from 28.2-134.5 microM against acetylcholinesterase, 16.0-23.1 microM against butyrylcholinesterase and 57.6-71.7 microM against lipoxygenase, respectively.

Acetylcholinesterase and butyrylcholinesterase inhibitory activity of some Turkish medicinal plants

The chloroform:medianol (1:1) extracts of a number of the plant species belonging to eight families, namely Corydalis solida (L.) Swartz subsp. solida and Glaucium corniculatum (L.) J. H. Rudolph (Papaveraceae), Rhododendron ponticum L. subsp. ponticum and Rhododendron luteum Sweet. (Ericaceae), Buxus sempervirens L. (Buxaceae), Vicia faba L. (Fabaceae), Robinia pseudoacacia L. (Caeselpiniaceae), Tribulus terrestris L. and Zygophyllum fabago L. (Zygophyllaceae), Lycopodium clavatum L. (Lycopodiaceae), Fumaria vaillantii Lois., Fumaria capreolata L., Fumaria kralikii Jordan, Fumaria asepala Boiss., Fumaria densiflora DC., Fumaria flabellata L., Fumaria petteri Reichb. subsp. thuretii (Boiss.) Pugsley, Fumaria macrocarpa Boiss. ex Hausskn., Fumaria cilicica Hauskkn., Fumaria parviflora Lam. and Fumaria judaica Boiss. (Fumariaceae) were screened for their anticholinesterase activity on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes by in vitro Ellman method at 10 microg/ml and 1 mg/ml concentrations. The extracts did not show any noticeable inhibitory activity against both of the enzymes at 10 microg/ml. The extracts of Rhododendron ponticum subsp. ponticum, Rhododendron luteum, Corydalis solida subsp. solida, Glaucium corniculatum, and Buxus sempervirens showed remarkable inhibitory activity above 50% inhibition rate on AChE at 1 mg/ml. Among them, Rhododendron ponticum subsp. ponticum, Corydalis solida subsp. solida and Buxus sempervirens were the most active extracts against BChE having 95.46 +/- 1.03%, 93.08 +/- 0.97%, and 93.45 +/- 0.88% inhibition rates, respectively. Among the extracts screened, all of the Fumaria extracts displayed highly potent inhibition against both of the enzymes at 1 mg/ml concentration compared to the standard.

Inhibition of sustained repetitive firing in cultured hippocampal neurons by an aqueous fraction isolated from Delphinium denudatum

In this report we investigated the effects of the aqueous fraction (AF) isolated from Delphinium denudatum on sustained repetitive firing in cultured neonatal rat hippocampal pyramidal neurons. Blockade of SRF is one of the basic mechanisms of antiepileptic drugs (AED) at the cellular level. The effects of aqueous fraction (0.2-0.6 mg/ml) were compared with the prototype antiepileptic drug, phenytoin (PHT). Using the whole cell current-clamp technique, sustained repetitive firing was elicited in neurons by a depolarizing pulse of 500 ms duration, 0.3 Hz and 0.1-0.6 nA current strength. Similar to phenytoin, aqueous fraction reduced the number of action potentials (AP) per pulse in a concentration-dependent manner until no action potentials were elicited for the remainder of the pulse. There was a corresponding use-dependent reduction in amplitude and Vmax (velocity of upstroke) of action potentials. The Vmax and amplitude of the first action potential was not affected by phenytoin, while aqueous fraction exhibited concentration-dependent reduction. At 0.6 mg/ml aqueous fraction reduced Vmax to 58-63% and amplitude to 16-20% of the control values. The blockade of sustained repetitive firing by aqueous fraction was reversed with hyperpolarization of membrane potential (-65 to -75 mV) while depolarization of membrane potential (-53 to -48 mV) potentiated the block. The results suggest that aqueous fraction blocks sustained repetitive firing in hippocampal neurons in a use-dependent and voltage-dependent manner similar to phenytoin. However, unlike phenytoin, which interacts preferably with the inactive state of the Na+ channel, the compounds present in aqueous fraction apparently also interact with the resting state of the Na+ channels as suggested by dose-dependent reduction of Vmax and amplitude of first AP. We conclude that aqueous fraction contains potent anticonvulsant compounds.

Quantitative HPLC analysis of withanolides in Withania somnifera

One of the most widely used herbs in Ayurvedic medicine is Ashwaghanda, Withania somnifera, a shrub commonly found on the Indian subcontinent. As this plant is increasingly becoming a popular adaptogenic in the western world, analytical methods for its identification and quality control are in demand. Thus, a HPLC method for the determination of withaferin A and withanolide D was developed. The system was successfully used to investigate the presence of the markers in different W. somnifera plant parts as well as to analyze their content in market products.

Anticonvulsant effect of FS-1 subfraction isolated from roots of Delphinim denudatum on hippocampal pyramidal neurons

The effects were investigated of a partially purified subfraction (FS-1) isolated from Delphinium denudatum on sustained repetitive firing (SRF) of cultured neonatal rat hippocampal pyramidal neurons. The blockade of sustained repetitive firing is one of the basic mechanisms of antiepileptic drugs at the cellular level. Using the whole cell current-clamp technique, sustained repetitive firing was elicited in pyramidal neurons under study by a depolarizing pulse of 500 ms duration, 0.3 Hz and 0.1-0.6 nA current strength. FS-1 (0.01-0.06 mg/mL) reduced the number of action potentials per pulse in a dose-dependent manner until no action potentials were elicited for the remainder of the pulse. There was a corresponding use-dependent reduction in amplitude and Vmax of action potentials. The Vmax of action potential 1 exhibited a dose-dependent reduction. At a dose of 0.06 mg/mL FS-1 reduced Vmax to 29%-38% and amplitude to 16%-20 % of the control values. The blockade of sustained repetitive firing by FS-1 was reversed by hyperpolarization of the membrane potential (-65 to -75 mV) while depolarization of the membrane potential (-53 mV to -48 mV) potentiated the block. The results suggest that FS-1 blocks sustained repetitive firing in hippocampal neurons in a use-dependent and voltage-dependent manner similar to the prototype anticonvulsant drug, phenytoin. However, unlike phenytoin, which binds preferably to the inactive state, the compounds present in FS-1 also interacted with the resting state of the Na+ channels by reducing Vmax of action potential 1. The results indicate that the partially purified FS-1 subfraction of Delphinium denudatum contains a potent anticonvulsant compound.

In vitro inhibition of pentylenetetrazole and bicuculline-induced epileptiform activity in rat hippocampal pyramidal neurons by aqueous fraction isolated from Delphinium denudatum

Roots of Delphinium denudatum W. are used for the treatment of epilepsy by traditional healers in subcontinent. Aqueous fraction (AF) isolated from D. denudatum has previously shown significant anticonvulsant activity in in vivo and in vitro models of seizures. We investigated anticonvulsant effects of AF on pentylenetetrazole (PTZ) and bicuculline (BIC)-induced epileptiform activity in primary hippocampal neuronal cultures. Electrophysiological studies on single pyramidal neurons were carried out by using whole-cell current clamp technique. Introduction of AF (0.6 mg/ml) in perfusate blocked PTZ (10 mM) and BIC (100 micro M)-induced epileptiform activity comprising of paroxysmal depolarization shifts (PDS). The PDS were elicited again when AF was removed from perfusate. We conclude that AF contains anticonvulsant compounds that possibly interact with GABA(A) receptor to produce blockade of epileptiform activity. Further studies on isolation of compounds from AF may lead to discovery of new class of anticonvulsants.

Chemistry and mechanism of urease inhibition

Studies on enzyme inhibition remain an important area of pharmaceutical research since these studies have led to the discoveries of drugs useful in a variety of physiological conditions. The enzyme inhibitors can interact with enzymes and block their activity towards natural substrates. Urease inhibitors have recently attracted much attention as potential new anti-ulcer drugs. Ironically, urease was the first enzyme crystallized but its mechanism of action is still largely misunderstood. This chapter therefore reviews comprehensive developments in the field of urease inhibitors. Inhibitors of urease can be broadly classified into two categories: (1) active site directed (substrate-like), (2) mechanism-based directed. We present here the examples of selected inhibitors along with their mechanisms of action to characterize their mode of urease inhibition. The observations that urease due to its high substrate (urea) specificity can only bind to a few inhibitors with a similar binding mode as urea is also discussed. Several non-covalent interactions including hydrogen bonds and hydrophobic contacts stabilize the enzyme-inhibitor complex. Regardless of the class of compound, it is reported that only a few functional groups with electronegative atoms such as oxygen, nitrogen and sulfur act either as bidentate (mostly), tridentate (rarely), or as ligand-chelator to form octahedral complexes with two slightly distorted octahedral Ni ions of the enzyme. Bulky groups attached to the pharmacophore were found to decrease the activity of inhibitors, since the lack of a bulky attachment makes it easier for urease inhibitors to enter the substrate-binding pocket as well as avoid unfavorable steric interactions with amino acid residues in its vicinity. This review is intended to provide highlights of the inhibition of urease by hydroxamic acids (HXAs), phosphorodiamidates (PPDs), imidazoles, phosphazene and related compounds. These compounds are compared to previously reported urease inhibitors for the catalytic models proposed for urease activity. The differences in inhibition of urease activities from plants and of bacterial origin by various inhibitors and physiological implications of urease inhibition are discussed.

Iso-N-formyl-5-en-chonemorphine, a steroidal alkaloid from Sarcococca zeylanica

Chemical investigation of the non-quaternary alkaloidal fraction of the aerial parts of Sarcococca zeylanica of the family Buxaceae furnished a steroidal alkaloid iso-N-formyl-5-en-chonemorphine, which has not been previously reported as a natural product. The structure of this alkaloid was established on the basis of spectroscopic evidence.

Antioxidant and antimicrobial activities of Tamarix ramosissima

The ethylacetate and water-acetone extracts of Tamarix ramosissima were screened for their antioxidant, antibacterial, antifungal and DNA damaging activities through in vitro experiments. All fractions as well as precipitates showed significant antioxidant activity. A known compound tamarixetin (1) was isolated which showed significant DNA damaging activity in mutant yeast bioassay. Results revealed that antioxidant and antibacterial activities were associated with the presence of polyphenolic substances.

Crystal structure of gamma-chymotrypsin in complex with 7-hydroxycoumarin

The 1.8 A crystal structure of 7-hydroxycoumarin (7-HC) bound to chymotrypsin reveals that this inhibitor forms a planar cinnamate acyl-enzyme complex. The phenyl ring of the bound inhibitor forms numerous van der Waals contacts in the S1 pocket of the enzyme, with the p-hydroxyl group donating a hydrogen bond to the main-chain oxygen atom of Ser217, and the o-hydroxyl group forming a water-mediated hydrogen bond with the carbonyl oxygen of Val227. The structure of the acyl-enzyme complex suggests that the mechanism of inhibition of 7-HC involves nucleophilic attack by the Ser195 O(gamma) atom on the carbonyl carbon atom of the inhibitor, accompanied by the breaking of the 2-pyrone ring of the inhibitor, and leading to the formation of a cinnamate acyl-enzyme derivative via a tetrahedral transition state. Comparisons with structures of photoreversible cinnamates bound to chymotrypsin reveal that although 7-HC interacts with the enzyme in a similar fashion, the binding of 7-HC to chymotrypsin takes place in a productive conformation in contrast to the photoreversible cinnamates. In summary, the 7-HC-chymotrypsin complex provides basic insight into the inhibition of chymotrypsin by natural coumarins and provides a structural basis for the design of more potent mechanism-based inhibitors against a wide range of biologically important chymotrypsin-like enzymes.

Anticonvulsant activities of ethanolic extract and aqueous fraction isolated from Delphinium denudatum

Dried roots of Delphinium denudatum Wall. are a popular folk remedy for the treatment of epilepsy in the traditional Unani system of medicine in the sub-continent. We carried out anticonvulsant screening of the ethanolic extract (EE) and aqueous fraction (AF) of this plant utilising the maximal electroshock (MEST) and subcutaneous pentylenetetrazole (scPTZ), bicuculline (scBIC), picrotoxin (scPTX) and strychnine (scSTN) tests for anticonvulsant activity. EE had weak dose-dependent anticonvulsant effects on seizures induced by PTZ and BIC. AF exhibited dose-dependent activity against hind limb tonic extension phase (HLTE) of MEST and comparatively stronger anticonvulsant activity against seizures induced by PTZ and BIC. The results suggest the presence of potent anticonvulsant compounds in AF of D. denudatum and deserve further investigation for isolation of active compounds and elucidation of the mechanism of anticonvulsant action.

Acetyl and butyrylcholinesterase-inhibiting triterpenoid alkaloids from Buxus papillosa

Three triterpenoid alkaloids, buxakashmiramine [(20S)-20-dimethylamino-4',6'-dimethoxy-5'-hydroxybenzoylamino-3beta-methyl-buxan-31-ol] (1), buxakarachiamine [(20S)-20-dimethylamino-2'-hydroxy-3beta-methyl-3'-methyl-butanoylamino-9,10-seco-buxa-9(11), 10(19)-dien-31-ol] (2) and buxahejramine [(20S)-20-dimethylamino-2'-hydroxy-3beta-methyl-3'-methyl-pentanoylamino-9,10-seco-buxa-9(11), 10(19)-dien-31-ol] (3) were isolated from the leaves of Buxus papillosa. Four known bases, cycloprotobuxine-C (4), cyclovirobuxeine-A (5), cyclomicrophylline-A (6) and semperviraminol (7) were isolated for the first time from this species. Their structures were established through extensive spectroscopic studies. Most of these compounds exhibited anticholinesterase activity.

Five new peltogynoids from underground parts of Iris bungei: a Mongolian medicinal plant

Five new peltogynoids, irisoids A-E (1-5), have been isolated from the underground parts of Iris bungei. The structures of the new compounds were established on the basis of spectroscopic methods and were found to be 1,8,10-trihydroxy-9-methoxy-[1]benzopyrano-[3,2-c][2]-benzopyran-7(5H)-one (1), 1,8-dihydroxy-9,10-dimethoxy-[1]benzopyrano-[3,2-c][2]-benzopyran-7(5H)-one (2), 1,10-dihydroxy-8,9-dimethoxy-[1]benzopyrano-13,2-c][2]-benzopyran-7(5H)-one (3), 1,8-dihydroxy-9,10-methylenedioxy-[1]benzopyrano-[3,2-c][2]-benzopyran-7(5H)-one (4), and 1,8,11-trihydroxy-9,10-methylenedioxy-[1]benzopyrano-[3,2-c][2]-benzopyran-7(5H)-one (5). The structure of irisoid B (2) was established unambiguously by X-ray diffraction study.

Anticonvulsant activities of the FS-1 subfraction isolated from roots of Delphinium denudatum

Delphinium denudatum Wall. (Ranunculaceae) is a medicinal herb used for the treatment of epilepsy in the subcontinent. The present study reports the anticonvulsant activities in the maximal electroshock test (MEST) and subcutaneous pentylenetetrazole (PTZ), bicuculline (BIC), picrotoxin (PIC)-induced seizures of the FS-1 subfraction (FS-1) that was obtained by purification of an aqueous fraction isolated from the roots of D. denudatum. In CF 1 mice, FS-1 (600 mg/kg i.p.) exhibited very potent anticonvulsant activity that was comparable to the effects of the well-known antiepileptic drug phenytoin (20 mg/kg) in MEST and protected 100% animals from hind limb tonic extension phase of this model. FS-1 also suppressed PTZ-induced threshold seizure and the loss of the righting reflex with tonic fore and hind limb extension by 100%, similar to the antiepileptic drug valproic acid (350 mg/kg). BIC-induced seizures were suppressed in 80% of the animals. FS-1 exhibited weak anticonvulsant effect on PIC-induced seizures, however, it significantly reduced mortality and delayed the onset of seizures. FS-1 had no effect on strychnine (STN)-induced extensor seizures. The results demonstrate the broad and potent anticonvulsant activity of the compounds in FS-1 of D. denudatum.

Four new flavones and a new isoflavone from Iris bungei

Four new irisflavones A-D (1-4) and irilin D (5) have been isolated from the underground parts of Iris bungei along with known isoflavones, irilins A-B (6-7) and tlatancuayin (8). The structures of the new compounds were determined using NMR and mass spectroscopic methods and were found to be 2',5,7-trihydroxy-3,6-dimethoxyflavone (1), 2',5-dihydroxy-3,6,7-trimethoxyflavone (2), 2',5,6'-trihydroxy-3,6,7-trimethoxyflavone (3), 3,3',5-trihydroxy-2',7-dimethoxyflavone (4), and 3',4',5,7-tetrahydroxy-6-methoxyisoflavone (5). The structures of irisflavones 1, 3, and 4 were confirmed by single-crystal X-ray diffraction studies.

Steroidal alkaloids from the leaves of Sarcococca coriacea of Nepalese origin

Two new steroidal alkaloids, (-)-vaganine D (1) [(20S)-20-(N,N-dimethylamino)-3 beta-(senecioylamino)-5 alpha-pregn-16-en-4 beta-yl acetate], and (+)-nepapakistamine A (2) [(20S)-20-(N-methylamino)-3 beta-(tigloylamino)-5 alpha-pregn-16-en-2 beta,4 beta-diacetate], were isolated from the leaves of Sarcococca coriacea. Their structures were elucidated on the basis of their spectral properties. Compounds 1 and 2 were found to be cholinesterase inhibitors.

New antioxidant and antimicrobial ellagic acid derivatives from Pteleopsis hylodendron

Bioassay-guided isolation of two new compounds, 3,4-methylenedioxy-3'-O-methyl-4'-O-glucoside ellagic acid (1) and the pteleoellagic acid derivative (2), from the stem bark of Pteleopsis hylodendron is reported along with 3,4-methylenedioxy-3'-O-methyl ellagic acid (3), 3,3'-di-O-methyl ellagic acid (4) and 3,3',4'-tri-O-methyl ellagic acid (5), which were obtained for the first time from this plant. The structures of these compounds were elucidated with the help of spectroscopic studies. Compounds 1 and 4 were found to have significant antioxidant activity, while compounds 1-4 showed antibacterial activity against different pathogenic bacteria.

Two new aurones from marine brown alga Spatoglossum variabile

Two new aurones, 4'-chloro-2-hydroxyaurone (1) and 4'-chloroaurone (2) were isolated from Spatoglossum variabile. The structures of these compounds were elucidated by modern spectroscopic techniques.

New norditerpenoid alkaloids from Aconitum falconeri

The roots of Aconitum falconeri have yielded two new norditerpenoid alkaloids, faleoconitine (1) and 3'-methoxyacoforestinine (2) along with the known compounds, karakoline, 3-hydroxy-2-methyl-4H-pyran-4-one, and 3,4-dimethoxymethylbenzoate, which have been isolated for the first time from this plant. The previously reported pseudaconitine (3) was also isolated. Compounds 1 and 3 were found to be moderate inhibitors of the enzyme acetylcholinesterase.

New steroidal alkaloids from Sarcococca saligna

Five new pregnane-type steroidal alkaloids (1-5) have been isolated from Sarcococca saligna. A combination of UV, IR, MS, and 1D and 2D NMR spectroscopic studies established their structures as salignarine A [(20S)-2beta-hydroxy-4beta-acetoxy-5alpha, 6alpha-epoxy-20-(dimethylamino)-3beta-(tigloylamino)pregnane ] (1), salignarine B [(20S)-2beta-hydroxy-20-(dimethylamino)-3beta-(tigloylamino) -pregn-5- ene] (2), salignarine C [(20S)-2beta-hydroxy-20-(dimethylamino)-3beta-(senecioylamino++ +)-pregn- 5-ene] (3), salignarine D [(20S)-20-(dimethylamino)-3beta-(senecioylamino)-5alpha-preg n-16-ene] (4), and salignarine E [(20S)-20-(dimethylamino)-3beta-(tigloylamino)-pregn-4-ene] (5), respectively.

Taraxacin, a new guaianolide from Taraxacum wallichii

A new guaianolide, taraxacin (1), and a known sesquiterpene ketolactone (2) have been isolated from an ethyl acetate-soluble part of a methanolic extract of Taraxacum wallichii. The structure of 1 was established using NMR, MS, and X-ray crystallographic methods. The (13)C NMR data of 2 is also being reported for the first time.