TLC–MS identification of alkaloids in Leonuri Herba and Leonuri Fructus aided by a newly developed universal derivatisation reagent optimised by the response surface method

Abstract

Introduction Dragendorff's reagent has low sensitivity and non‐specificity for some alkaloids. A new alkaloid derivatisation reagent has been developed and optimised by using a Box–Behnken design method. This new reagent is applicable for structurally diverse natural alkaloids, and is proposed as a universal alkaloid staining reagent. Objective To establish an efficient and sensitive thin‐layer chromatography (TLC) identification method for Leonuri Herba and Leonuri Fructus to characterise their differences and similarities. Method Three key components (bismuth subnitrate, potassium iodide and iodine) in the derivatisation reaction were re‐constructed and optimised using a response surface method. Different inorganic acids, essential additives of the staining reaction, were compared by a single‐factor experiment design. Results This newly optimised reagent for alkaloids reported in this study, named the enhanced Dragendorff–Wagner's reagent, is composed of 0.82% bismuth subnitrate, 11.1% potassium iodide and 0.76% iodine in 38% phosphoric acid solution. Validation results indicate that the TLC spot of stachydrine stained with the enhanced Dragendorff–Wagner's reagent had a limit of detection of 2.0 μg, good intra‐ and inter‐plate, and intra‐ and intra‐day precisions with relative standard devition values less than 5.0%, and stability over 90 min. Conclusion This enhanced Dragendorff–Wagner's reagent was applied for TLC identification of 16 reference alkaloids representing 11 structural skeletons, and two closely related herbs (Leonuri Herba and Leonuri Fructus). This newly enhanced Dragendorff–Wagner's reagent is a universal, effective, and sensitive staining reagent for alkaloids.

Structurally Diverse Bisbenzylisoquinoline Alkaloids with Antiadipogenic Activity through PPARγ Downregulation from the Embryo of Nelumbo nucifera Seeds

“…Compound 1 was isolated as a pink amorphous powder, with a positive result to Dragendorff’s reagent (orange red), indicating the presence of an alkaloid skeleton. , HRESIMS and 13 C NMR (Table ) analyses revealed a molecular formula of C 39 H 44 N 2 O 6 at m / z 637.3269 [M + H] + (calcd for C 39 H 45 N 2 O 6 , 637.3272). The 1 H NMR spectrum (Table ) revealed two N -methyl signals at δ H 2.84 and 2.87, four aromatic proton singlets at δ H 6.88, 6.81, 6.53, and 6.00, corresponding to two 1,2,4,5-tetra-substituted aromatic rings, a pair of doublets at δ H 6.73 (2H, d, J = 8.4 Hz) and 6.96 (2H, d, J = 8.3 Hz) of an AA′BB′ system, and an ABX system with δ H 6.33 (1H, d, J = 1.9 Hz), 6.75 (1H, d, J = 8.4 Hz), and 6.78 (1H, dd, J = 8.3, 1.9 Hz).…”

Stachydrine and Synephrine, a Pair of Bioactive Equilibrists in Four Chinese Herbs from <em>Citrus</em> Genus

“…Generally, two chromogenic reagents Dragendorff's and Wagner were used for the color reaction of most alkaloids, while they present poor effects for some alkaloids with small molecular weight. Considering acidic environment should be provided for the color reaction, the acetic acid was replaced as phosphoric acid in Dragendorff's reagent for improving the chromogenic sensitivity, referring what Zhang N, et al reported [72]. Moreover, if the color of spots is red, such as orange red or brownish red, the compounds represented by the spots are likely not choline analogs, while are likely alkaloids, possibly some polymethoxy flavonoids, or polymethoxybenzenes (such as α-and β-asarones) since the potassium bismuth iodide reagent colors these compounds to orange red or brownish red.…”

Histochemical Localization of Alkaloids in the Bulbs of In Vitro-Regenerated Snake’s Head Fritillary (Fritillaria meleagris L.): The Effect of a Temperature Regime

“…The presence of alkaloids was detected by Wagner's or Dragendorff's reagents [27], which produce a golden-brown-or reddish-brown-colored reaction in response to alkaloids, respectively (the intensity of staining depends on the quantity of alkaloids). Wagner's reagent (iodine potassium iodide solution) was prepared by dissolving 2 g I 2 and 6 g KI in 100 mL of distilled water.…”