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        Blue Thunbergia Leaf is the dried leaf of Thunbergia laurifolia Lindl. (Family  Acanthaceae), Herbarium Specimen Number:  BKF 160078, Crude Drug Number:  DMSc 0688.

Constituents  Blue Thunbergia Leaf contains caffeic acid, flavonoids, sterols, etc.

Description of the plant  (Figs. 1a, 1b)  Climber to woody climber; s tem terete, glabrous to glabrescent. Leaves simple, opposite, oblong to ovate, 5 to 19 cm long, 2.5 to 9 cm wide, apex acute to acuminate, base cuneate, obtuse, truncate, or subcordate, margin entire or slightly crenate to dentate, basal veins 3 to 5, prominent on lower surface, both surfaces scabrous, glabrous or sparsely hispidulous, dark green above, lighter green beneath; petiole 1.5 to 6 cm long, sparsely hispidulous to nearly glabrous. Inflorescence pendulous, axillary or terminal raceme, 4 to 30 cm long; pedicel 1.5 to 3 cm long; bracteoles 2, ovate-lanceolate, 2 to 4.5 cm long, 1 to 2 cm wide, apex obtuse to acute, green with violet blotches. Flower blue to violet, showy, 6 to 8 cm in diameter; calyx green, 3 mm long, puberulous; corolla broadly funnelform, lobes 5, 3 to 4.5 cm long; s tamens 4, didynamous, filaments puberulous; ovary superior, 2-loculed, each with 2 axile ovules, s tyle 1, s tigma 2-lobed. Fruit capsule, subglobose at base, about 1.5 cm long, about 1.0 cm wide, with a s tout beak of 2 cm long at the tip, splitting through the beak into 2 pieces. Seeds 1 or 2 per locule, plano-convex, about 1 cm in diameter.

Description  Odour, mild; taste, bland.

      Macroscopical  (Fig. 1a)  A mixture of entire and broken, brown to dark brown, oblong to ovate leaves.

       Microscopical  (Figs. 2a, 2b, 2c)  Transverse sections of the leaf through the midrib and the lamina show upper epidermis, a layer of elongated rectangular cells, irregular and  wavy-walled in surface view; diacytic stomata; glandular trichome, unicellular stalk,  2-celled head; non-glandular trichome, unicellular.  Lower epidermis, wavy-walled in  surface view; diacytic stomata, numerous; glandular trichome, a few.  Mesophyll, 2 or 3 layers of columnar palisade cells and several layers of irregular spongy cells.  Underneath both epidermises, few layers of collenchyma cells associated with vascular tissues in the midrib.  Vascular bundle, phloem in the upper part and xylem in the lower part, surrounded by bundle sheaths.  Some bundle sheaths and parenchyma cells containing acicular crystals.  Vessels, spiral, reticulate and pitted.

         Blue Thunbergia Leaf in powder possesses the diagnostic microscopical characters of the unground drug.

Warning  Concomitant use with other drugs should be avoided since it may increase the excretion of the other drugs.

Additional information  Ethnomedically, it has been used orally as a first-aid detoxificant.  A use of 10 to 15 fresh or dried partially mature leaves, ground with sufficient amount of Nam Sao Khao (water washings from uncooked rice) or water, and squeezed to obtain about one tablespoonful of the extract, is suggested.

Packging and storage  Blue Thunbergia Leaf shall be kept in well-closed containers,  protected from light, and stored in a dry place.

Identification

       A. Reflux 200 mg of the sample, in powder, with 10 mL of chloroform for 15 minutes and  filter.  Evaporate 2 mL of the filtrate to dryness in a test-tube.  Dissolve the residue in 1 mL of acetic anhydride, cautiously add 1 mL of sulfuric acid to form two layers:  a reddish brown colour forms at the zone of contact and the upper layer is green.

       B. Heat 200 mg of the sample, in powder, with 10 mL of water in a water-bath for  10 minutes and filter.  To 2 mL of the filtrate, add a few drops of iron(III) chloride TS:   a greenish blue colour with precipitate is produced.

       C. Carry out the test as described in the “Thin-Layer Chromatography” (Appendix 3.1), using silica gel G as the coating substance and a mixture of 70 volumes of chloroform,  30 volumes of methanol and 5 volumes of formic acid as the mobile phase and allowing the  solvent front to ascend 10 cm above the line of application.  Apply separately to the plate  as bands of 8 mm, 8 μL of solution (A) and 3 μL of solution (B).  Prepare solution (A) by  refluxing 500 mg of the sample, in powder, with 25 mL of water for 30 minutes, filtering  and evaporating to dryness.  Dissolve the residue in 5 mL of a 50 per cent v/v solution of  methanol.  For solution (B), dissolve 1 mg of caffeic acid in 5 mL of a 50 per cent v/v solution of methanol.  After removal of the plate, allow it to dry in air.  Heat the plate at 80° for 10 minutes and then spray with natural products (NP) TS while the plate is still warm. Subsequently spray the plate with polyethyleneglycol (PEG) TS and observe the colours of  the bands under ultraviolet light (366 nm) through the cut-off filter within 5 to 15 minutes.  The chromatogram obtained from solution (A) shows an intense blue fluorescent band (hR_f value 83 to 90) corresponding to the caffeic acid band from solution (B).  Several fluorescent bands of different colours also appear (Table 1); see also Fig. 3.

Table 1 hR_f Values of Components in Water Extract of the Leaves of Thunbergia laurifolia Lindl.

       *caffeic acid

Loss on drying  Not more than 9.0 per cent w/w after drying at 105° to constant weight (Appendix 4.15).

Foreign matter  Not more than 2.0 per cent w/w (Appendix 7.2).

Acid-insoluble ash  Not more than 11.0 per cent w/w (Appendix 7.6).

Total ash  Not more than 23.0 per cent w/w (Appendix 7.7).

Ethanol-soluble extractive  Not less than 5.0 per cent w/w (Appendix 7.12).

Water-soluble extractive  Not less than 14.0 per cent w/w (Appendix 7.12).