Chemistry of South African Lamiaceae: Structures and Biological Activity of Terpenoids

Abstract

South Africa flora is one of the most important mega floras with high endemic species percentage. Lamiaceae is an important family in South Africa with ±308 species in 41 genera and contains many important plants (~23%) traditionally used for treatment of different human diseases. The chemical profile of Lamiaceae is very rich in terpenoids in general and more specifically diterpenes. Genera like Leonotis and Plectranthus are well studied, while on the other hand, genus like Stachys (~41 species, ~50% endemic) didn’t receive any attention. Different classes of diterpenes were identified and some of them demonstrating important biological activities.

This work is dedicated to Prof. Benjamin Rodriguez (Instituto de Quimica Organic General, CSIC, Spain) for his contributions in the field of natural products and specially in the chemistry of Lamiaceae family.

1. Introduction

The Green economy concept has been driven as an urgent need for addressing global challenges in vital fields like energy, environment, and health. Green economy is expected to play a very important role in changing the way that society manages the interaction of the environmental and economic domains. Consequently, a new paradigm has been established and shifted toward green economy or green growth. Natural products represent one of the most important elements required to build safe and effective economy especially in health sector. South Africa (SA) is recognized as one of the most biodiverse country in the world with 20,456 indigenous vascular plant taxa recorded where 13,265 (65%) are endemic [1, 2].

The Lamiaceae (formerly Labiateae, mint family) is a cosmopolitan family with ~7136 species in 236 genera. Most species are shrubby or herbaceous and trees are extremely rare [3]. The Lamiaceae family has great economic value, as it contains several horticultural species, most of which are used as culinary herbs like salvia, rosemary, ocimum, mint, Leonotis, etc. Lamiaceae species are known to contain pharmacologically active terpenoids with a wide spectrum of bioactivity and expected to play more important roles in the process of drug discovery as well as cosmetic, food, and pesticides industries [4, 5, 6]. In the Sub-Saharan region, ~60 genera with ±980 species were reported [7]. SA considers as a diversity spot of Lamiaceae with ±308 species in 41 genera [8]. The species occur predominantly in the summer and/or winter rainfall areas. The habitats are different and vary to a great extent [9].

However, the South African flora is one of the most important mega floras for its unique diversity and endemism, it receives low attention in terms of bioprospecting, and the number of research paper every year dealing with chemical/biological profiling is still beyond the required level. This review serves as a background for the chemistry of all species belonging to the family Lamiaceae growing in SA and it covers publications till 2017. The articles information’s abstracted from Sci-finder database [10] and includes all species growing in SA as well as other places. This chapter doesn’t cover the essential oils and Plectranthus barbatus, which recently reviewed by others [11, 12].

2. Terpenoids of different genera of South African Lamiaceae

Different classes of secondary metabolites have been identified from Lamiaceae, the majority of the isolated compounds are terpenoids (~71%), and additionally other classes of compounds like flavonoids, α-pyrone derivatives, phenolic acids, and alkaloids were reported. Mono-, sesqui-, and tri-terpenoids are relatively small in number (~15%) when compared to diterpenoids and it was reported that more than 100 of different diterpene skeletons were identified which indicate the high evolutionary index of Lamiaceae [13]. According to the literature, the genera Leonotis (known as wild dagga) and Plectranthus have received the highest attention where 70 (Leonotis) and 94 (Plectranthus) compounds were identified so far, the majority of the isolated compounds are labdane diterpenes. In this chapter, the different genera have been listed alphabetically and the trivial names have been retained in the cases where they were given by authors and/or chemical abstracts.

2.1. Aeollanthus genus

Aeollanthus genus represented by 43 species globally and 7 in SA. From A. buchnerianus, an abie-tane diterpene, [(rel)-14α-acetoxyabiet-7-en-18-oic acid] (1) [14], 3β-acetoxy-7,15-isopimaradiene (2), 3β-acetoxy-7,15-isopimaradien-19-ol (3) and 19-acetoxy-7,15-isopimaradien-3β-ol (4), 7,15-isopimaradien-19-ol (5, akhdarenol) and 7,15-isopimaradien-3β,19-diol (6, virescenol), a mixture of 19-isobutyryloxy- and 19-butyryloxy-8β-hydroxy-15-isopimarene (7), and a 3:1 mixture of 5-stigmasten-3β-ol and β-sitosterol were isolated from the aerial parts of A. rydingianus. 5 and 6 showed activity against S. aureus and Enterococcus hirae [15].

2.2. Ballota genus

Ballota is represented by one species in SA vizB africana. Hispanolone (8) was isolated from the aerial parts [16].

2.3. Cedronella genus

Cedronella genus is represented by only one species in SA viz C. canariensis. The phytochemical studies of the aerial parts resulted in isolation of a dimer of d-pinocarvone (9), cedronellone (10), and ursolic acid (11) [17].

2.4. Clerodendrum genus

Seven species were recorded in SA and clerodendrumic acid (12) was isolated from C. glabrum var. glabrum and showed weak antifungal, antibacterial, and cytotoxic activities [18].

2.5. Hoslundia genus

Hoslundia genus is represented by one species in SA vizH. opposite. The phytochemical studies of the aerial parts yielded an interesting and rare pyrano and furanoflavonoid derivatives in addition to euscaphic and (13) ursolic acid (11) [19, 20]; four abietane-type esters, 3-O-cinnamoylhosloppone (14), 3-O-benzoylhosloppone (15), 3-O-benzoylhosloquin-one (16), and 3-O-benzoylhinokiol (17); 13 was found to exhibit MIC of 50 μg/mL against M. tuberculosis, while 14 inhibits the growth of the MDR strain K₁ of Plasmodium falciparum in vitro with an IC₅₀-value of 0.4 μg/mL [21].

2.6. Hyptis genus

Three species were recorded in SA. The triterpenes 3α,19α-dihydroxyurs-12-en-28-oic acid (18) and 3β-acetoxyoleanan-13β,28-olide (19), Me betulinate (20), oleanolic acid/acetate (21/22), and ursolic (11) and maslinic acids (23) were isolated from H. mutabilis [22].

From H. spicigera, seven labdane diterpenes; 19-acetoxy-2α,7α,15-trihydroxylabda-8(17),(13Z)-diene (24); 15,19-diacetoxy-2α,7α-dihydroxylabda-8(17),(13Z)-diene (25); 7α,15,19-triacetoxy-2α-hydroxylabda-8(17),(13Z)-diene (26); 19-acetoxy-2α,7α-dihydroxylabda-8(17),(13Z)-dien-15-al (27); 19-acetoxy-7α,15-dihydroxylabda-8(17),(13Z)-dien-2-one (28); 2α,7α,15,19-tetrahydroxy-ent-labda-8(17), (13Z)-diene (29); and 19-acetoxy-2R,7R-dihydroxylabda-14,15-dinorlabd-8(17)-en-13-one (30) were isolated from the aerial parts [23].

2.7. Leonotis genus

Seven species were recorded in SA and two of them were extensively studied. Traditionally, this genus is used to substitute hemp and called as wild dagga; however, there is no much scientific biological evidences supporting such claim. The chemistry was started in early 60s of the last century by South African researchers. Many labdane diterpenes have been isolated. The chemistry of the genus was covered previously by a review published by Piozzi et al.[24].

2.7.1. Leonotis leonurus

The chemistry of Leonotis was commenced in 1962 and some compounds were identified; marrubiin (31) compounds, X (32) and Y (33), the stereoisomers of premarrubiin (34) and (35) (the C-13 epimeric forms of premarrubiin). Leonurun (36) has been isolated and the relative stereochemistry was determined using single-crystal X-ray diffraction analysis [24, 25]. After two years, labdane (13S)-9α,13α-epoxylabda-6β(19),15(14)-dioldilactone (37) was isolated, this compound caused significant changes in blood pressure of anesthetized normotensive rats, and also was found to exhibit a negative chronotropic effect [26].

The organic extract of L. leonurus showed 99% growth inhibition against M. tuberculosis at 1.0 mg/mL, subsequent phytochemical studies resulted in the identification of three labdane-type diterpenoids: 9,13:15,16-diepoxy-6,16-labdanediol (38), 6-acetoxy-9,13-epoxy-15-methoxy-labdan-16,15-olide (39), and 9,13-epoxy-6-hydroxylabdan-16,15-olide (40). None of the isolated compounds were active against M. tuberculosis [27].

Recently, Fang et al. [28] identified leonurenones A–C (41–43), in addition to 9,13:15,16-diepoxy-6,16-labdanediol (38) and nepetifolin (44). The leonurenones contain an uncommon α,β-unsaturated enone moiety in ring B. Compound 38 was isolated as epimeric form, (at C-16, ratio 3:1). Compound 41 was isolated from aqueous extract of the leaves and the authors proposed the possible formation of 43 as an artefact via oxidation and lactonization of the more polar intermediate (41) during the isolation process. The total aqueous extract, at concentration of 1.0 g/mL, showed an 81% inhibition in a binding assay at the GABAA site. Compounds 41 and 43 did not show activity (<50% inhibition) in this assay [28].

In the following year, Wu and co-workers (2013) were successful to isolate and identify eleven labdanoides, viz leoleorins D–J (41–43, 45–48) and 16-epi-leoleorin F (49), leoleorin A [corresponding to compound Y (33)], leoleorin B (50) (anhydro derivative of compound Y), and leoleorin C [9,13-epoxy-6-hydroxylabdan-15,16-olide (40)]. The absolute configurations of leoleorin A (33) and D (41) were established by X-ray crystallographic analyses. It is important to indicate that new compounds “leoleorins G-I”, which were isolated in this study, were reported in the previous work under the names of leonurenones A–C (41–43) (¹³C data showed exchange positions C₁₂ and C₁₄ for leonurenones C/leoleorin H between the two references) [29].

From L. leonurus’ flowers, an acyclic diterpene ester, 1,2,3-trihydroxy-3,7,11,15-tetramethylhexadecan-1-yl-palmitate (51), along with geniposidic acid (52) were isolated, the compounds exhibited neither cytotoxicity on mammalian kidney fibroblasts (Vero cells) nor antimicrobial activities [30].

2.7.2. Leonotis nepetaefolia

The chemistry of L. nepetaefolia started almost simultaneously with L. leonurus. Leonotin (53), nepetaefuran (54), nepetaefuranol (55), nepetaefolin (44) methoxynepetaefolin (56), nepetaefolinol (57) and leonotinin (58) the dilactone (8β,17,9,13-diepoxylabdane-16,15,19,6β-diolactone, 59) were characterized [31, 32, 33, 34, 35, 36].

From the species collected from India, nepetaefolinol (57), dehydrated nepetaefolinol (60) and isomeric tetrol (61) (15,16-epoxy-labda-13(16),14-diene-6β,9,17,19-tetrol: the reduction product of leonotinin) were identified [37]. Leonitinic acid (62) with free C-17 carboxyl group was also isolated [38].

From a commercially material, originally collected from Peru, five inseparable epimeric mixtures of bis-spirolabdane diterpenoids, resulted from biosynthetic epimerization of three different structures around C-13 and C-15, have been isolated and identified as leonepetaefolin A (63) and its epimeric isomer 15-epi-leonepetaefolin A (64) (ratio 1:1), leonepetaefolin B(65)/15-epi-leonepetaefolin B (66) (2:3), leonepetaefolin C(67)/15-epi-leonepetaefolin C (68) (1,1), leonepetaefolin D (69)/15-epi-leonepetaefolin D (70) (7,10), leonepetaefolin E (71)/15-epi-leonepetaefolin E (72) (2,3) [39]. Additionally, methoxynepataefolin (56), nepetaefolin (44), nepetaefuran (54), dubiin (73), 19 chlroro derivative of nepetaefolin (74), leonotinin (58), leonotin (53), and LS-1 (75) were isolated. The absolute configuration of the epimeric mixture 63 and 64 was determined by X-ray crystallographic analysis [39].

The isolated compounds were evaluated for their binding activities to a panel of CNS G-protein-coupled receptors including adrenergic, dopaminergic, histaminic, muscarinic, opioid, and serotonergic receptors and neurotransmitter transporters and showed no interesting activity.[39]. From the material collected from Japan, five iridoid glycosides: 10-O-(trans-3,4-dimethoxycinnamoyl) geniposidic acid (76), 10-O-(p-hydroxybenzoyl) geniposidic acid (77), geniposidic acid (52), mussaenoside (78), and ixoside (79) were isolated [40].

2.7.3. Leonotis ocymifolia

L. ocymifolia was studied under different synonyms viz; L. dubia (L. ocymifolia, var. ocymifolia),L. leonitis; L. leonitis var. hirtfolia (L. ocymifolia, var. ocymifolia) and L. dysophylla Benth. (L. ocymifolia var. raineriana) and L. ocymifolia var. raineriana (Burm f) Iwarsson var. raineriana (Visiani) Iwarsson. The chemical studies resulted in the isolation of dubiin (73), 9α,13(S)-epoxy-8β-hydroxylabdane-6β,19;16,15-diolide (80), and leonitin (81). 20-acetoxy-9α,l3-dihydroxy-15(16)-epoxylabd-14-en-6β(19)-lactone (82) and 6β-acetoxy-9α,l3α-epoxylabda-20(19),16(15)-diol-dilactone (83) are from the leaves, in addition to compound X (32)[24, 41] Finally, nepetaefolin (44), leonotinin (58), and leonotin (53) were identified from the material collected from Pretoria (South Africa) [42].

2.8. Neophyptis genus

Neophyptis genus is represented by N paniculata in SA. Isoneocembrene-A (84), β-caryophyllene oxide(85), α-himachalene (86), the isolates showed weak to moderate antibacterial activity against five strains of S. aureus [43].

2.9. Ocimum genus

Ocimum genus comprises 65 aromatic species, distributed in tropical and subtropical regions worldwide. Species belonging to this genus are popularly used in Africa and Asia for treating diabetic symptoms. The genus is represented by 16 species in SA and the phytochemical study of O. amercanium afforded four compounds of the copane series (copan-3-ol (87), cop-l1(12)-en-3-o1 (88), cop-3(15)-en-11-ol (89), and cop-l0(ll)-en-3,12-diol(90)) [44].

2.10. Orthosiphon genus

Orthosiphon genus comprises 40 species recorded from the old world: in tropical and subtropical regions including Southern Africa and Madagascar. Three species were found in SA. Three labdanoids (+)-trans-ozic acid (91), labda-8(17),12E,14-trien-2α,18-diol (92), and 2α-hydroxylabda-8(17),12E,14-trien-18-oic acid (93) have been isolated from an ethanol extract. Compound 93 exhibited activity against M. tuberculosis, while 92 showed cytotoxic activity against MCF-7 and decreased the production of all the pro-inflammatory cytokines. From the same source, pheophytin a, the acidic degradation product of chlorophyll a, was isolated and showed inhibition of HIV-1 protease [45, 46].

2.11. Paltstoma genus

Only one species was recorded in SA. From the ethyl acetate extract of P. rotundifolium, cassipourol (94), β-sitosterol, and α-amyrin were identified [47].

2.12. Plectranthus genus

About 300 species distributed in tropical and warm regions of the old World, 45 species recorded in SA, from which 19 species were studied for their chemical and/or biological constituents. The genus is characterized by the presence of orange glands that distributed in the aerial parts and contain highly oxygenated (and modified) abietane-type diterpenoids. Others, e.g., kaurane, labdane, phyllocladane as well as the rare skeleton halimane diterpenoids were described.

2.12.1. Plectranthus ambiguus

Plectranthus ambiguus afforded a series of tetracyclic phyllocladane-type (= 13β-kaurane) diter-penoids: (16R)-2α-senecioyloxy-3α-acetoxyphyllocladan-16,17-diol (95), (16R)-2α-senecioyloxy-3α,17-diacetoxy-16-hydroxyphyllocladane (96), (16R)-2α-isovaleroyloxy-3α-acetoxyphyllocladan-16,17-diol (97), (16R)-2α-isovaleroyloxy-3α,17-diacetoxy-16-hydroxyphyllocladane (98), (16R)-3α-acetoxyphyllocladan-16,17-diol (99), (16R)-2α-senecioyloxy-16,17-dihydroxyphyllocladan-3-one (100), and (16R)-2α,3α-diacetoxyphyllocladan-16,17-diol (101). The authors discriminated between phyllocladane and ent-kaurane tetracyclic skeletons after extensive spectroscopic investigation as well as chemical transformations [48, 49].

2.12.2. Plectranthus amboinicus

Thymoquinone (105) was identified as an active nonpolar ingredient to suppress the expression of lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-α) [50]. The total extract showed cytotoxic activity against MCF-7, using HPLC-based metabolomics approach, and 7α-acetoxy-6β-hydroxyroyleanone (102) was identified as the main active constituent. Other minor compounds like coleon E (103) and royleanone (104) were also identified [51].

2.12.3. Plectranthus caninus

Plectranthus caninus afforded coleons M (106), N (107), P (108), Q(109), R (110), S (111), and T (112) and barbatusin (113) [52, 53].

2.12.4. Plectranthus ecklonii

Plectranthus ecklonii is traditionally used in South Africa for treating stomach aches, nausea, vomiting, and meningitis. Ecklonoquinone A (114) and B (115) and parviflorons D (116) and F (117) were isolated [54, 55]. Compound 117 showed potent activity against Listeria monocytogenes and M. tuberculosis and both 116 and 117 were found to be very toxic against vero cell lines. The potency of parvifloron D (116) was further confirmed and showed fast and potent apoptotic inducer in leukemia cells [56].

2.12.5. Plectranthus ernstii

Two pimaranes rel-15(ζ),16-epoxy-7α-hydroxypimar-8,14-ene (118): rel-15(ζ),16-epoxy-7-oxopimar-8,14-ene (119) and a labdane 1R,11S-dihydroxy-8R,13R-epoxylabd-14-ene (120) were isolated. The three compounds showed activity against M. tuberculosis and different strains of S. aureus [57].

2.12.6. Plectranthus fruticosus

Plectranthus fruticosus cultivated in Porugal afforded 4 labdanes, ent-labda-8(17),12Z,14-trien-2β-ol (121),ent-2α-acetoxylabda-8(17),12Z,14-trien-3β-ol (122), ent-3β-acetoxylabda-8(17),12Z,14-trien-2α-ol (123),3β-acetoxylabda-8(17),12E,14-trien-2α-ol (124), 10 kauranes (ent-12β-acetoxy-15β,16β-epoxykauran-19-oic acid (125), ent-7β-hydroxy-15β,16β-epoxykauran-19-oic acid (126), ent-15β,16β-epoxykauran-19-oic acid (127), ent-15β,16β-epoxykauran-19-ol (128), ent-12β-acetoxy-15β-hydroxykaur-16-en-19-oic acid (129), ent-12β-acetoxy-7β-hydroxykaur-16-en-19-oic acid (130),methyl ent-12β-acetoxy-16-kauren-19-oate (131), ent-7β-hydroxykaur-15-en-19-oic acid (132), methyl ent-12β-acetoxy-7β-hydroxykaur-15-en-19-oate acid (133), ent-12β-acetoxy-17-oxokaur-15-en-19-oic acid (134), methyl ent-12β-acetoxy-15-kauren-19-oate (135), additionally, armendrance (136), caryophyllene α-oxide (137), ursolic/oleanolic acids (2,1 mixture) β-sitosterol, stigmasta-5,22E-dien-3β-ol, and β-amyrin. Some of the compounds showed moderate anti-staphylococcus activity [58, 59]. P. fruticosus growing in India showed abietane diterpene pattern and 7α-acetoxy-6β-hydroxyroyleanone (102), 6,7-dehydroroyleanone (138) and 7α,6β-dihydroxyroyleanone (139) were isolated [60].

2.12.7. Plectranthus grandidentatus

In addition to 14-hydroxytaxodione (140), coleons U (141) and V (142), a series of abietane dimers namely grandidone A (143), B(145), and D(147) and their epimers 7-epigrandidone A(144), B(146), and D (148) and grandidone C (149) [61] were identified. Also, royleanone (103), 6,7-dehydroroyleanone (138), horminone (150), 6β-hydroxyroyleanone (151), and 7α-acetoxy-6β-hydroxyroyleanone (102) together with a mixture of fatty acid esters of 7α-acyloxy-6β,12-dihydroxy-abieta-8,12-diene-11,14-dione (152), 7α,6β,-dihydroxyroyleanone (139), and 9α-(2-oxopropyl)abietane derivative(156) were isolated [62, 63, 64, 65, 66, 67].

Fatty acid esters of 7α-acyloxy-6β-hydroxyroyleanone (152) showed moderate antibacterial activity [62]; coleon U exhibited potent cytotoxicity against a panel of human cancer cell lines [63, 65] also showed potent inhibition of mouse splenocyte proliferation induced by ConA or LPS mitogens [64]. Coleons U 141 is considered as a promising compound and deserves further evaluation as an anti-cancer drug [68]. Coleon U (141), 7α-acetoxy-6β-hydroxyroyleanone (102), and horminone (150) showed activity against methicillin-resistant S. aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VRE). Recently, the biological activity of 102 was reported and showed selective cytotoxicity against MCF-7. Other derivatives of the same compound showed potent cytotoxic [69, 70] and antimicrobial [66] activities.

2.12.8. Plectranthus hereroensis

Plectranthus hereroensis horminone (150), 16-acetoxy-7α,12-dihydroxy-8,12-abietadiene-11,14-dione (153) and 7α-12-dihydroxy-17(15→16)-abieta-8,12,16-triene-11,14-dione (157);3β-acetoxy-6β,7α-12-trihydroxy-17(15→16)18(4→3)bisabeo-abieta-4(19)8,12,16-triene-11,14-dione (158) were isolated [13, 66, 71], on the other hand, the structure of an aristolane sesquiterpene aldehyde (159) have been revised [72], all compounds showed moderate antimicrobial activity [13, 66, 71, 72], while 158 showed antiviral activity [73].

2.12.9. Plectranthus madagascariensis

Plectranthus madagascariensis is used as a traditional medicine in Southern Africa. Three constituents were isolated and identified as 6β,7β-dihydroxyroyleanone (154), 7β-acetoxy-6β-hydroxyroyleanone (155), and coleon U (141). The compounds exhibited inhibitory activity on α-glucosidase, S. aureus and Enterococcus faecalis [74].

2.12.10. Plectranthus ornatus

Traditionally, the plants were used for treatment of stomach and liver diseases and as a substitute of P. barbatus. The phytochemical studies resulted in the isolation of 11 neoclerodanes (plec-trornatins A (160) [75], 11R*-acetoxykolavenic acid (161), 11R*-acetoxy-2-oxokolavenic acid (162), 11R*-acetoxy-3β-hydroxyneocleroda-4(18),13E-dien-15-oic acid (163) [76], ornatins A–E (164-168), 3β-hydroxyneocleroda-4(18),13E-dien-15-oic acid (169) [77]; 7 labdanes (plectrornatins B (170), C (171), [75],6-O-acetylforskolin (172); 1,6-di-O-acetylforskolin (173), 1,6-di-O-acetyl-9-deoxyforskolin (174) [76, 78], rhinocerotinoic acid (175) [66], 8β-hydroxylabd-13-en-15-oic acid (176) [77]); 2 abietanes (14-O-acetyl-coleon U (177), coleon R (110)) and a halimane derivative, (11R*-acetoxyhalima-5,13E-dien-15-oic acid (178) [79]) in addition to β-sitosterol and stigmasterol, 3β-acetyl-α-amyrin, and friedelin. Inversion at C-13 of 1,6-di-O-acetyl-9-deoxyforskolin (174) was carried out based on correlations between ¹³C NMR experimental data and HF/6-31G* calculation [80]. 160, 161 showed moderate antimicrobial. 178 exhibited growth inhibitory activity against five Staphylococcus and five Enterococcus strains [75]. Ornatin C, D, E and three related diterpenes displayed marginal bactericidal or bacteriostatic effects against the Gram-positive strains [77].

2.12.11. Plectranthus porcatus

Plectranthus porcatus: (13S,15S)-6β,7α,12α,19-tetrahydroxy-13β,16-cyclo-8-abietene-11,14-dione (179) has been isolated and showed weak antibacterial activity against S. aureus [81].

2.12.12. Plectranthus saccatus

Plectranthus Saccatus ent-7α-acetoxy-15-beyeren-18-oic acid (180), ent-3β-(3-methyl-2-butenoyl) oxy-15-beyeren-19-oic acid (181), and ent-3β-(3-methylbutanoyl) oxy-15-beyeren-19-oic acid (182). Both 181 and 182 showed insect antifeedant activity against Spodopteralittoralis, while 180 showed no antibacterial activity [81, 82].

2.12.13. Plectranthus strigosus

Plectranthus strigosus: 9 abietanes (parviflorones A (183), B (184), C (185), D (114), E (186), F (115), G (187), and H (188) [83], and hinokiol (189)) [84]), 3 kauranes (ent-16-kauren-19-ol (190), ent-16-kauren-19-oic acid (191), xylopic acid (192), xylopinic acid (193)), and 2 sesquiterpens (4β,6β-dihydroxy-1α,5β(H)-guai-9-ene (194) 4β,6β-dihydroxy-1α,5β(H)-guai-10(14)-ene (195)), were isolated [84]. A bioactivity study revealed herpetic inhibitory properties for (190) and (191) [84].

2.13. Salvia genus

The genus Salvia is known as sage and is the largest genus in Lamiaceae, comprising over 900 species distributed throughout the world. Salvia is represented by 30 species in SA, distributed mainly in great cape region. The chemistry of Salvia is rich in diterpenoids and different skeletons have been reported, also, many members of this genus is well known for its curative and medicinal properties like S. officinalis and S. miltiorrhiza.

2.13.1. Salvia africana-lutea

Salvia africana-lutea: carnosol (196), rosmadial (197), and carnosic acid (198-characterized as its methyl ester) were isolated. Compound 198 exhibited potent activity against M. tuberculosis and cytotoxic activity against a breast (MCF-7) human cancer cell line [45].

2.13.2. Salvia chamelaeagnea

Salvia chamelaeagnea: four compounds were isolated: carnosol (196), 7-O-methylepirosmanol (200), oleanolic and ursolic acids as the active principles against S. aureus [85].

2.13.3. Salvia coccinea

Salvia coccinea: momordic acid, methyl ester (201) [86], salviacoccin (202) [87], dehydrouvaol (203), and uvaol (204) [88] were isolated.

2.13.4. Salvia disermas

Salvia disermas aerial parts afforded ocotillol II (205) [89].

2.13.5. Salvia radula

Salvia radula: betulafolientriol oxide (206) was isolated [90].

2.13.6. Salvia reflexa

Salvia reflexa: four neoclerodanes were isolated and identified as salviarin (207), 6β-hydroxysalviarin (208), 15,16-epoxy-8α-hydroxyneocleroda-2,13(16),14-triene-17,12R:18,19-diolide (209), and 5,6-secoclerodane, 7,8-didehydrorhyacophiline (210) [91].

2.13.7. Salvia repens

S. repens whole plant extract yielded 12-methoxycarnosic acid (199) with antiprotozoal activity against Leishmania donovani amastigotes and cytotoxicity against the L6-cells [92].

2.13.8. Salvia verbenaca

Salvia verbenaca yielded β-sitosterol, ursolic acid, dehydroursolic acid, sitosteryl-3-β-D-glucoside [93], taxodione (211), horminone (150) and 7α-acetoxy-6β-hydroxyroyleanone (102) [94], verbenacine (212) and salvinine (213) [95].

2.14. Solenostemon genus

Solenostemon genus is from S. rotundifolius; oleanolic acid was isolated as a major component [96].

2.15. Tetradenia genus

Seven species were recorded in SA, one of them T. riparia is widely distributed in Africa and showed interesting chemical profile. Several compounds have been isolated from the leaves of this plant, including 8(14),15-sandaracopimaradiene-7α,18-diol (214) [97], 8(14),15-sandaracopimaradiene-2α,18-diol (215) [98], 9β,13β-epoxy-7-abietene (216), 6,7-dehydroroyleanone (136) [99], and ibozol (217) [100].

Compound (214) exhibited antimicrobial activity (213). Compound (215) showed papaverine-like antispasmodic activity on guinea pig ileum contracted by methacholine, histamine, or BaCl₂ and on the noradrenaline-induced contractions of rabbit aorta [101]. It also showed activities against Trichomonasvulgaris with MIC of 20–40 μg/mL [102], wheat rootlets inhibition activity (MIC7.81 μg/mL) [103], and M. tuberculosis[104].

2.16. Teucrium genus

Three species were recorded in SA. From T. africanumtafricanins A (218) and B(219), teutrifidin (220) and 4α,18-epoxytafricanin A (221) were isolated [105].

2.17. Vitex genus

Vitex genus is represented by 12 species in SA. The fraction responsible for antimicrobial activity of V. rehmannii was purified to give a labdane diterpene as an inseparable epimeric mixture of 12S,16S/R-dihydroxy-ent-labda-7,13-dien-15,16-olide (222). The extract and the labdane diterpene exhibited good antimalarial activity, with the labdane diterpene being the most active IC₅₀: 2.39 ± 0.64 μg/mL [106].

3. Conclusion

South African flora characterized by high endemism and unique floral kingdom is only located in the great cape region. Lamiaceae is represented by ~308 species widely distributed all over the country. In general, the bioprospecting of SA flora including Lamiaceae is not reached; yet the required level and more attention are required to explore the potential of their chemical constituents. The present work shades the light on the isolated terpenoids of all listed species in updated SA flora checklist. It is interesting to indicate that Plectranthus genus contains mostly abietane diterpenes and shows potent activity as demonstrated by coleon U and parviflorons F and D. On the other hand, leoleorin C from L. Leonurus showed moderate binding affinity (Ki = 2.9 μM) to the Sigma 1 receptor. These compounds and others may be considered as a model for drug discovery for human benefits.

Acknowledgments

Cape Peninsula University of Technology and National Research Foundation, South Africa, (grant No. 106055).

Conflict of interest

The author declares no conflict of interest to disclose.