Enaam Y. Backheet

Selective spectrophotometric method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices

A simple and selective method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices is described. The procedure is based on the reaction of ascorbic acid with the zinc chloride salt of diazotized 1-aminoanthraquinone (Fast Red AL salt) in an acidic medium, followed by development of a blue colour (λmax 630 nm) in alkaline solution. Different variables affecting the colour development were studied and optimized. The method was used to determine between 5 and 25 µg ml–1 of ascorbic acid in the final measured solution. The simplicity of the method permits rapid analysis, suitable for routine control. The method is highly specific for the determination of ascorbic acid in the presence of dehydroascorbic acid and all other vitamins normally encountered with it in pharmaceutical dosage forms. Moreover, the proposed method can also be applied to the determination of ascorbic acid in some fresh fruit juices without interference from coloured and other substances present in the fruit extracts. The reliability of the method was established by parallel determinations against the official British pharmacopoeial method.

Antiparasitic antioxidant phenylpropanoids and iridoid glycosides from Tecoma mollis.

A radical scavenging guided phytochemical study on the stem bark of Tecoma mollis afforded seven active phenylpropanoid glycosides (1-7), including a new one (4), and one iridoid (8). The structures of the isolated compounds were elucidated on the basis of spectroscopic evidences and correlated with known compounds. Compounds (1-7) displayed promising antioxidant activity (DPPH assay) in relation to ascorbic acid (positive control). The antimicrobial activity for compounds (1-8) was evaluated against five bacterial and five fungal strains. The isolated compounds exhibited nonselective weak to moderate antimicrobial activity. The highest antileishmanial activity against Leishmania donovani was observed for compound (7) with an IC₅₀ value of 6.71 μg/ml, using pentamidine and amphotericin B as drug controls. Compound (5) exhibited moderate antimalarial activity (45% inhibition) against chloroquine sensitive (D6) clones of Plasmodium falciparum.

Isoflavonoids and flavone glycosides from rhizomes of Iris carthaliniae

Abstract Two new isoflavonoid biosides, tectorigenin 4′-glucosyl (1→6)glucoside and iristectorigenin B 7-glucosyl (1→6)glucoside, a new isoflavonoid monoside, 4′-methyltectorigenin 7-glucoside and a new flavone glucoside, 6,4′-dimethoxy-5-hydroxyflavone 7-glucoside, together with tectoridin and tectorigenin 4′-glucoside were isolated from rhizomes of Iris carthaliniae . The structures of the isolated compounds were determined by NMR spectral analysis.

Three hydroxymethylanthraquinone glycosides from rubia tinctorum

Three hydroxymethylanthraquinone glycosides, in addition to the known compounds alizarin, lucidin-ω-ethyl ether, lucidin primeveroside and the iridoid asperuloside were isolated from the dried roots of Rubia tinctorum. The first three compounds were isolated for the first time from this species. The structures were established as 1-hydroxy-2-hydroxymethylanthraquinone 3-glucoside, 2-hydroxymethylanthraquinone 3-glucoside and 3,8-dihdroxy-2-hydroxymethylanthraquinone 3-glucoside.

A selective spectrophotometric method for determination of quercetin in the presence of other flavonoids.

A simple, rapid and highly selective method for determination of quercetin in the presence of other flavonoids was developed. The method is based on the oxidation reaction of quercetin in neutral aqueous solution with N-bromosuccinimide (NBS) in the presence of phenol to give a violet chromogen measurable at 510 nm. Beers law was valid within a concentration range of 2.5-30 mug/ml with a good correlation coefficient (r = 0.9990). All variables were studied to optimize the reaction conditions. The method is highly selective for quercetin. Other investigated flavonoids do not interfere. Mixtures of flavonoids were also analysed through native UV measurements of absorbance readings at 370 nm and then at 510 mn after adopting the proposed procedure. The method could also be utilized for the quantitative determination of quercetin in some plant extracts. Moreover, the proposed procedure could be considered as a good tool to follow the hydrolysis of quercetin glycosides.

Two new acetylated flavonoid glycosides from Centaurium spicatum L

Two new acetylated flavonol glycosides, quercetin 3-O-[(2,4-diacetyl-α-l-rhamnopyranosyl)-(1→6)]-2,4-diacetyl-β-d-galactopyranoside (1) and quercetin 3-O-[(2,4-diacetyl-α-l-rhamnopyranosyl)-(1→6)]-3,4-diacetyl-β-d-galactopyranoside (2), in addition to two known acetylated quercetin glycosides quercetin 3-O-[(2,3,4-triacetyl-α-l-rhamnopyranosyl)-(1→6)-β-d-galactopyranoside (3) and quercetin 3-O-[(2,3,4-triacetyl-α-l-rhamnopyranosyl)-(1→6)-3-acetyl-β-d-galactopyranoside (4), were isolated from the aerial part of Centaurium spicatum (L.) Fritsch (Gentianaceae). Structure elucidation, especially the localization of the acetyl groups, and complete 1H and 13C NMR assignments of these biologically active compounds were carried out using one- and two-dimensional NMR measurements, including 1H- and 13C-NMR, DEPT-135, H–H COSY, HMQC and HMBC, in addition to HR-FAB/MS experiments.

New cycloartane saponin and monoterpenoid glucoindole alkaloids from Mussaenda luteola

A new cycloartane-type saponin with unusual hydroxylation at C-17 and a unique side chain, 9 (R), 19, 22 (S), 24 (R) bicyclolanost-3β, 12α, 16β, 17α tetrol-25-one 3-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside (1) and two new monoterpenoid glucoindole alkaloids, 10-methoxy pumiloside (2) and the previously chemically synthesized, 10-methoxy strictosidine (3) along with other five known compounds, 7α-morroniside (4), 7-epi-loganin (5), (7β)-7-O-methylmorroniside (6), 5(S)-5-carboxystrictisidine (7) and apigenin-7-O-neohesperidoside (8) were isolated from the aerial parts of Mussaenda luteola (Rubiaceae). The structural elucidation of the isolates was accomplished by extensive (1D and 2D NMR) spectroscopic data analysis and HR-ESI-MS. Compounds 4-8 were reported for the first time from the genus Mussaenda. Interestingly, this is the first report for the occurrence of the monoterpenoid glucoindole-type alkaloids in the genus which might be useful for the chemotaxonomic evaluation of the genus Mussaenda. All isolates were evaluated for their antiprotozoal activities. Compound 7 showed good antitrypanosomal activity with IC50 and IC90 values of 13.7 and 16.6 μM compared to IC50 and IC90 values of 13.06 and 28.99 μM for the positive control DFMO, difluoromethylornithine.

Use of haematoxylin in the spectrophotometric determination of alkaloids in pharmaceuticals, galenicals and powdered plants

A simple and sensitive method for the determination of about fifteen alkaloids is described. The procedure is based on the reaction of the alkaloids with haematoxylin reagent in aqueous medium to give a red–violet colour (λmax= 555 nm). Several variables affecting the colour development were studied and optimized. The method was used to determine 2–40 µg ml–1 of the final measured alkaloidal base solution. There was a considerable increase in the absorptivity, which was dependent on both the basicity (pKa) and molar concentration of the alkaloid present. The simplicity of the method permits rapid analysis, suitable for routine quality control. The interference of about 28 substances which are commonly prescribed with alkaloids was studied. No interference due to additives commonly present in the pharmaceutical preparations was observed. The method could be applied for the analysis of alkaloids in pure and pharmaceutical dosage forms, galenicals and powdered plants.

Cinnamyl Alcohol, Benzyl Alcohol, and Flavonoid Glycosides from Sanchezia nobilis

Further phytochemical investigation of Sanchezia nobilis Hook.f. (Acanthaceae) has afforded nine compounds, the cinnamyl alcohol glycosides: 9-O-β-glucopyranosyl trans-cinnamyl alcohol (1), 9-O-β-xylopyranosyl-(1→6)-O-β-glucopyranosyl-(1→6)-O-β-glucopyranosyl trans-cinnamyl alcohol (2), and syringin (3); the neolignan glucoside: 4-O-β-glucopyranosyl dehydrodiconiferyl alcohol (4); the benzyl alcohol glycosides: 7-O-β-glucopyranosyl benzyl alcohol (5) and 7-O-β-apiofuranosyl-(1→6)-O-β-glucopyranosyl benzyl alcohol (6), together with the flavonoid glycosides: apigenin-7-O-β-glucopyranoside (7), apigenin-7-Ogentiobioside (8), and apigenin-7-O-β-glucuronopyranoside (9). Compound 2 is isolated here for the first time from a natural source, compounds 1, 3, 4, and 8 have been isolated for the first time from the family Acanthaceae, while compounds 5–7 and 9 are reported for the first time from the genus Sanchezia.