Asaad Khalid

Cholinesterase inhibitory and spasmolytic potential of steroidal alkaloids.

A new steroidal alkaloid, isosarcodine (1) along with four known bases, sarcorine (2), sarcodine (3), sarcocine (4) and alkaloid-C (5) were isolated from the MeOH extract of Sarcococca saligna. The structures of these alkaloids were identified by spectral data interpretation. These compounds were subjected to acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition studies, and were found to be noncompetitive inhibitors of AChE (Ki = 21.8, 90.3, 32.2, 16.0 and 50.0 microM, respectively) and uncompetitive or noncompetitive inhibitors of BChE (Ki = 8.3, 7.5, 15.6, 5.0 and 12.0 microM, respectively). The compounds (2-5) also showed dose-dependent spasmolytic activity in the rabbit jejunum intestinal preparations and also relaxed the high K+ (80 mM)-induced contraction, indicative of a calcium channel-blocking mechanism. Structure-activity relationship suggested that the nitrogen substituents at C-3 and/or C-20 of steroidal skeleton and the hydrophobic properties of the pregnane skeleton are the key structural features contributed to the inhibitory potency of these steroidal alkaloids against AChE and BChE.

Muscarinic, Ca++ antagonist and specific butyrylcholinesterase inhibitory activity of dried ginger extract might explain its use in dementia

Ginger rhizome (Zingiber officinale) has been used for centuries to treat dementia in South Asia. This study was undertaken to possibly justify its use. A 70% aqueous/methanolic extract of dried ginger (Zo.Cr) was used. Zo.Cr tested positive for the presence of terpenoids, flavonoids, secondary amines, phenols, alkaloids and saponins. When tested on isolated rat stomach fundus, Zo.Cr showed a spasmogenic effect (0.03–5.00 mg mL−1); it relaxed the tissue at concentrations ≥5 mg mL−1. The stimulant effect was resistant to blockade by hexamethonium and methysergide, but sensitive to atropine, indicating activity via muscarinic receptors. In atropinized (0.1 μM) preparations, Zo.Cr (0.3–3.0 mg mL−1) relaxed high K+ (80 mm)‐induced contractions, indicating Ca++ antagonism in addition to the muscarinic effect. This possible Ca++ antagonist activity was investigated in Ca++‐free conditions, with the inhibitory effect of the extract tested against contractions induced by externally administered Ca++. Zo.Cr (0.1–0.3 mg mL−1), similar to verapamil (0.03–0.10 μm), shifted the contractions induced by externally administered Ca++ to the right, thus suggesting an inhibitory interaction between Zo.Cr and voltage‐operated Ca++ channels. Zo.Cr (0.1–3.0 μg mL−1) also potentiated acetylcholine peak responses in stomach fundus, similar to physostigmine, a cholinesterase inhibitor. Zo.Cr, in an in‐vitro assay, showed specific inhibition of butyrylcholinesterase (BuChE) rather than acetylcholinesterase enzyme. Different pure compounds of ginger also showed spasmolytic activity in stomach fundus, with 6‐gingerol being the most potent. 6‐Gingerol also showed a specific anti‐BuChE effect. This study shows a unique combination of muscarinic, possible Ca++ antagonist and BuChE inhibitory activities of dried ginger, indicating its benefit in dementia, including Alzheimers disease.

New natural cholinesterase inhibiting and calcium channel blocking quinoline alkaloids

During this study, one new coumarin; 7-O-β-D-glucopyranoside-2H-1-benzopyran-2-one (1) and three quinoline alkaloids; 3-hydroxy, 2, 2, 6-trimethyl–3, 4, 5, 6-tetrahydro-2H-pyrano[3,2-c] quinoline 5-one (2), ribalinine (3) and methyl isoplatydesmine (4) were isolated from the aerial parts of Skimmia laureola and their structures established by spectroscopic studies. Compounds 2-4 were found to be linear mixed type inhibitors of acetylcholinesterase (Ki = 110.0, 30.0 and 30.0 μM, respectively). Compounds 2 and 3 were also found to be linear mixed type inhibitors of butyrylcholinesterase, while compound 4 was a noncompetitive inhibitor of the enzyme (Ki = 90.0, 70.0 and 19.0 μM, respectively). The inhibition of acetyl- and butyryl-cholinesterase enzymes persists as the most promising therapeutic strategy for activating the impaired cholinergic functions in Alzheimers disease and related dementias. Compound 4 also showed dose-dependent spasmolytic activity in the isolated rabbit jejunum intestinal preparation by relaxing the spontaneous (EC50 = 0.1 mg/mL) and K+-induced contractions (EC50 = 0.4 mg/mL), suggesting that the spasmolytic effect of compound 4 is mediated through the blockade of voltage-dependent Ca2 + channels.

Pregnane-Type Steroidal Alkaloids of Sarcococca saligna: a New Class of Cholinesterase Inhibitors

Phytochemical investigation of Sarcococca saligna by extensive bioassay-guided fractionation resulted in the isolation of the pregnane-type steroidal alkaloids 1–15, i.e. of the five new compounds 1–5 and the ten known alkaloids 6–15. The structures of the new alkaloids salignenamide C (1), salignenamide D (2), 2β-hydroxyepipachysamine D (3), salignenamide E (4), and salignenamide F (5) were elucidated with the help of modern spectroscopic techniques, while the known alkaloids axillarine C (6), axillarine F (7), sarcorine (8), N3-demethylsaracodine (9), saligcinnamide (10), salignenamide A (11), vaganine A (12), axillaridine A (13), sarsalignone (14), and sarsalignenone (15) were identified by comparing their spectral data with those reported earlier. Inhibition of electric-eel acetylcholinesterase (EC 3.1.1.7) and horse-serum butyrylcholinesterase (EC 3.1.1.8) by alkaloids 1–15 were investigated. These new cholinesterase inhibitors may act as potential leads in the discovery of clinically useful inhibitors for nervous-system disorders, particularly by reducing memory deficiency in Alzheimers disease patients by potentiating and effecting the cholinergic transmission process. These compounds were found to inhibit both enzymes in a concentration-dependent fashion with the IC50 values ranging from 5.21–227.92 μM against acetylcholinesterase and 2.18–38.36 μM against butyrylcholinesterase.

Methylenebissantin: A rare methylene-bridged bisflavonoid from Dodonaea viscosa which inhibits Plasmodium falciparum enoyl-ACP reductase

A new methylene-bridged bisflavonoid, methylenebissantin (1), and nine known compounds, including flavonoids (2-5), diterpenoids (6 and 7), and phenol derivatives (8-10) were isolated from the aerial parts of Dodonaea viscosa Jacq. The structure elucidation was based on spectroscopic data analyses. The isolated compounds were evaluated for the inhibition of Plasmodium falciparum enoyl-ACP reductase (PfENR). Methylenebissantin (1) exhibited a moderate inhibition (IC(50) 91.13 μM) against PfENR.

Phytochemical and enzyme inhibitory studies on indigenous medicinal plant Rhazya stricta.

A new triterpenoid 3α-hydroxy-ursane-5-ene (1) and a known steroid stigma sterol (2) have been isolated for the first time from the fruit of Rhazya stricta. The structures of these compounds were elucidated and identified by spectral studies. The crude ethanolic extract of R. stricta fruit has led to the determination of good results of antibacterial, lipoxygenase and acetylcholinesterase activities. In addition, we also reported the acetylcholinesterase activity of stigma sterol (2) isolated from this plant. Stigma sterol (2) was found to be an acetyl-cholinesterase inhibitor with IC50 at a concentration of 644.0 ± 11.75 µM. Eserine [(−)-physostigmine, IC50 = 61 nM)] was used as a positive control.

A new fatty ester and a new triterpene from Skimmia laureola

Aerial parts of Skimmia laureola yielded a new fatty ester, (+)-skimmilaureol (1), and a new triterpene 16-29-dihydroxy, 20-ene cyclolaudenol (2). Five known compounds, namely, O-methyl-cyclolaudenol (3), (R)-7-methoxy-6-(3′-hydroxy-2′R-methoxy-3′-methyl butyl)coumarin (4), (+)-(S)-ψ-ribalinine (5), (R)-(+)-ribalinine (6) and methyl isoplatydesmine (7), previously isolated from this plant were subjected to enzymatic bioassays for the first time. Compounds 3 and 4 were found to be prolyl endopeptidase inhibitors with IC50 8.21 ± 0.407 and 39.63 ± 1.502 µM, respectively, while compounds 5–7 were found to be acetyl-cholinesterase and butyryl-cholinesterase inhibitors with IC50 62.46 ± 1.58, 153.31 ± 1.9, 74.5 ± 1.05 and 150.04 ± 0.45, 12.99 ± 0.31, 78.3 ± 1.86 µM, respectively.

Antimycobacterial activity of selected medicinal plants traditionally used in Sudan to treat infectious diseases

ETHNOPHARMACOLOGICAL RELEVANCE The emergence of multidrug-resistant strains of Mycobacterium tuberculosis underscores the need for continuous development of new and efficient methods to determine the susceptibility of isolates of Mycobacterium tuberculosis in the search for novel antimycobacterial agents. Natural products constitute an important source of new drugs, and design and implementation of antimycobacterial susceptibility testing methods are necessary to evaluate the different extracts and compounds. In this study we have explored the antimycobacterial properties of 50 ethanolic extracts from different parts of 46 selected medicinal plants traditionally used in Sudan to treat infectious diseases. MATERIALS AND METHODS Plants were harvested and ethanolic extracts were prepared. For selected extracts, fractionation with hydrophilic and hydrophobic solvents was undertaken. A luminometry-based assay was used for determination of mycobacterial growth in broth cultures and inside primary human macrophages in the presence or absence of plant extracts and fractions of extracts. Cytotoxicity was also assessed for active fractions of plant extracts. RESULTS Of the tested extracts, three exhibited a significant inhibitory effect on an avirulent strain of Mycobacterium tubercluosis (H37Ra) at the initial screening doses (125 and 6.25µg/ml). These were bark and leaf extracts of Khaya senegalensis and the leaf extract of Rosmarinus officinalis L. Further fractions of these plant extracts were prepared with n-hexane, chloroform, ethyl acetate, n-butanol, ethanol and water, and the activity of these extracts was retained in hydrophobic fractions. Cytotoxicity assays revealed that the chloroform fraction of Khaya senegalensis bark was non-toxic to human monocyte-derived macrophages and other cell types at the concentrations used and hence, further analysis, including assessment of IC50 and intracellular activity was done with this fraction. CONCLUSION These results encourage further investigations to identify the active compound(s) within the chloroform fraction of Khaya senegalensis bark.