The Phytochemistry and Pharmacology of Tulbaghia, Allium, Crinum and Cyrtanthus: 'Talented' Taxa from the Amaryllidaceae

Abstract

Amaryllidaceae is a significant source of bioactive phytochemicals with a strong propensity to develop new drugs. The genera Allium, Tulbaghia, Cyrtanthus and Crinum biosynthesize novel alkaloids and other phytochemicals with traditional and pharmacological uses. Amaryllidaceae biomolecules exhibit multiple pharmacological activities such as antioxidant, antimicrobial, and immunomodulatory effects. Traditionally, natural products from Amaryllidaceae are utilized to treat non-communicable and infectious human diseases. Galanthamine, a drug from this family, is clinically relevant in treating the neurocognitive disorder, Alzheimer's disease, which underscores the importance of the Amaryllidaceae alkaloids. Although Amaryllidaceae provide a plethora of biologically active compounds, there is tardiness in their development into clinically pliable medicines. Other genera, including Cyrtanthus and Tulbaghia, have received little attention as potential sources of promising drug candidates. Given the reciprocal relationship of the increasing burden of human diseases and limited availability of medicinal therapies, more rapid drug discovery and development are desirable. To expedite clinically relevant drug development, we present here evidence on bioactive compounds from the genera Allium, Tulgbaghia, Cyrtanthus and Crinum and describe their traditional and pharmacological applications.

Keywords: Allium; Amaryllidaceae; Crinum; Cyrtanthus; Tulbaghia; alkaloids; drug discovery; natural products; pharmacological activity; phytochemicals.

Figure 1

Chemical space of compounds identified from T. violacea. Blue circles are sulfur-containing compounds while red circles are compounds devoid of sulfur in their chemical structures. PCA analysis carried out using DataWarrior [54].

Figure 2

Analysis of cLogP and molecular weight space occupied by compounds identified in T. violacea. Blue circles are sulfur-containing compounds while red circles are compounds devoid of sulfur in their chemical structures. Plot generated using DataWarrior [54].

Figure 3

Chemical structures of compounds identified in T. violacea. (1) Marasmicin (1), (2) marasmin (2), allicin (3)—possesses antibacterial and antifungal activity, d-fructofuranosyl-β(2→6)-methyl-α-d-glucopyranoside (4), β-d-fructofuranosyl-(2→6)-α-d-glucopyranoside (5), methyl-α-d-glucopyranoside (6), bis(methylthiomethyl) disulfide (7)—found to constitute 48% of volatiles in aerial parts of T. violacea [55], methyl-2-thioethyl thiomethyl trisulfide (8)—found to constitute 16% of volatile compounds in aerial parts of T. violacea [55], methyl (methylthio)methyl disulfide (9)—found to constitute 10 % of volatile compounds in aerial parts of T. violacea [55], naphthalene (10)—interestingly observed to significantly increase in concentration in plants infected by the fungus Beauveria bassiana in comparison to untreated controls [59], nonanal (11)—also observed to significantly decrease in concentration in plants infected by the fungi Beauveria bassiana in comparison to untreated controls [59] and finally kaempferol (12)—which possesses multiple biological activities including antioxidant, anticancer and anti-inflammatory properties [60,61,62].

Figure 4

Chemical structures of compounds isolated from the genus Allium. Quercetin (13), vanillic acid (14) and adenosine (15).

Figure 5

Chemical structures of compounds isolated from the genus Crinum. Lycorine (16), crinamine (17), galantamine (18) and crinine (19).

Figure 6

Chemical structures of selected compounds from Crytanthus. Zephyranthine (20), 1,2-O-diacetylzephyranthine (21), haemanthamine (22), haemanthadine (23), galanthamine (18), 5,7-dihydroxy-6-methoxy-3-(4ꞌ-methoxybenzyl)chroman-4-one (24), 5,7-dihydroxy-6-methoxy-3-(4ꞌ-methoxybenzylidene)chroman-4-one (25), 5,7-dihydroxy-6-methoxy-3-(4ꞌhydroxybenzyl)chroman-4-one (26), 5,7-dihydroxy-3-(4ꞌhydroxybenzylidene)-chroman-4-one (27) and naciprimine (28).