S. Afr. J. Bot. 2000, 66(1): 7-9 7

A convenient thin layer chromatographic technique for chemotaxonomic application in Maytenus ()

C. B. Rogers*, A.T.D. Abbotll and A. E. van Wyk2 *Department of Chemistry. University of Durban-Westville. Private Bag X54001 , Durban, 4000 Republic of South Africa 1P.O . Box 111 , Port Edward. 4295 Republic of South Africa 2H.G .W .J Schweickerdt Herbarium, Department of Botany, University of Pretoria, Pretoria. 0002 Republic of South Africa

Received .J August 1998: rev1sed I 5 December 1998

The genus Maytenus in southern Africa is replete with taxonomic problems, both at specific and supra-specific levels. Chemical data in taxonomy are an important adjunct to morphological evidence as it reflects on relationships of at another level of structural organization. In this study fourteen species of Maytenus (mainly from the Pondoland Centre of endemism) have been used to test the applicability of an easy-to-use thin layer chromatographic (TLC) technique. Leaf extracts provided chemical 'fingerprints' which were diagnostic for each species. Chemical evidence thus obtained also supports the reinstatement of the segregate genus . The technique described holds considerable promise, not only for resolving classification problems in Maytenus, but also for taxonomic application in other groups of plants.

Keywords: Celastraceae, chemotaxonomy, Gymnosporia, Maytenus, taxonomy, thin layer chromatography.

·To whom correspondence should be addressed, (E-mail: [email protected]).

Introduction GPm aluminium backed plates using I(JUr sol vent systems or ~ar~­ Floristically the sandstone region of southern KwaZulu-Natal ing polarity. Solutions were applied to plates in bands I em wide and Pondoland has been identified as a distinct centre of ende­ (two or three applications) and allowed to develop t<1r 9 em . For mism , called the Pondoland Centre (PC). With thirteen species some species, the composition of the extract is so distinctive that the the PC is particularly rich in species of Maytenus; of w hich at TLC from a single solvent system (SIS) is suflicient to provide a least four are considered endemic to the region (Van Wyk 1990). "tingerprint' that is diagnostic for that species. For other species As currently c ircumscribed, the genus Maytenus is clearly an extracts may need to be analysed by several SIS's to establish the chemical uniqueness of the species. heterogeneous assemblage, perhaps worthy of splitting into a In this study the fo llowing fou r solvent systems were used: light number of more natural genera. Furthermore, interspecific petroleum:ethyl acetate (8:3. vl v). for the separation of non-polar boundaries in some of the closely-knit species complexes are constituents: light petroleum:ethyl acetate:chloroform:lormic acid often vague and in dispute (Van Wyk & A rcher 1987). (8:7:5: 1, v/v), for the separation of constituents of intermediate Hitherto, a wide variety of secondary metabolites such asses­ polarity; and either chloroform:ethyl acetate: formic acid (5:4: I . vlv) quiterpenoids, triterpenoids, alkal oids and flavonoids have been or chloroform:methanol:water ( 12:3: I . vl v-lower layer). lor the sep­ isolated from members of in other parts of the world Maytenus aration of polar constituents. A spray reagent consisting of p-anisal­ (e.g. Bruning & Wagner 1978; Nozaki eta/. t 986; Gonzalez et dehyde (5 ml), cone. sulphuric acid (5 ml) and ethan ol (90 ml) was Here we test the hy pothesis that this variety of second­ a/. 1993 ). used to visualise colourless constituents: these appeared as coloured ary metabol ites is species specific and could be used as chemical bands after the sprayed plate had been heated at t l0°C I(H 2-5 min­ evidence to aid in the identification and classification of the utes. Apart from Rf comparisons. the most diagnostically important group. Thin layer chromatographic (TLC) fingerprinting of the information in this technique is provided h~ 1·ariations or similarities acidic triterpenoid fraction of leaf extracts in the genus Combre­ tum (Combretaceae) has been used extensively to resolve taxo­ nomic problems in this gen.us (Carr & Rogers 1987; Rogers & Coombes 1999). In t~~ present study we explore the potential taxonomic significanq-e of a similar TLC technique in selected southern African members of the genus Maytenus.

Materials and Methods Fourteen species of Maylenus, mostly from the PC, were studied in the summer of 1986187 (Table I). Leaf samples were collected from the Umtamvuna Nature Reserve in southern KwaZulu-Natal, except for those of M. Iucida, which came from the Western Cape Province (Cape Point Nature Reserve). V oucher specimens are deposited in the H.G.W..J. Schweickerdt Herbarium (PRU), University of Preto­ r ia. Fresh leaves(± 10 g) were immersed in methanol (100 ml) over­ night at room temperature. The methanolic solution was decanted from the leaves and concentrated under vacuum; residual water was removed from the extract by azeotropic distillation with benzene (2 1 2 3 4 5 6 7 8 9 10 11 12 13 x 20 ml). TLC analyses on solutions from each extract [50 mg ml·1 Figure 1 Representative TLC tingerprints of extracts developed chloroform:ethanol (I: I, vlv)] were carried out on Merck silica gel in the non-polar SIS; light petroleum:ethyl acetate (8:3 v/ v). ll S. Afr. J. Bot. 2000. 66( I )

Table 1 Species of Maytenus investigated: TLC track No's; voucher specimen numbers (all collected by A.T.D. Abbott); and percentage yield of extract TI .C Collectors Track No. No. Species %yield of extract (fresh leaves) 5766 M abbolfii VanWyk 18.9

2 5767 M. acuminata (L.f.) Loes 24.7

5768 AI. sp. A(== Gymnosporiafiliformis Davison p.p.) 12.8 -1 5769 A.f. sp. 8 (= Gymnosporia heterophyl/a (Eckl. & Zeyh.) Loes] 17.9 5 5770 M. nws.wmbicensis (Kiotzsch) Blakelock 24.8

577 1 M. sp. C (== Gymnosporia uniflora Davison) 21.9 7 5772 M. umlara (Thunb.) Blakelock 22.5 l! 5775 ,'.f. procwnbens (L. t:) Loes 16.4 9 5774 M. cordata (E. Mey. ex Sond.) Loes. 23.2

10 5776 M. peduncularis (Sond.) Locs. 9.8 II 5777 M. heterophylla (Eckl. & Zeyh.) N.K.B. Robson s. l. [= Gymnosporia 2 1.7 buxifolia (L.) Szyszy l.] 12 57KR M. bachmannii (Loes. ) Marais [= Gymnosporia bachmannii (Loes.) 12.0 Szyszyl.]

13 5789 ,l,f. oleosa Van Wyk & Archer 24.8

14 4432 M. Iucida (L.) Locs. dried leaves extracted: yield not relevant in the colour of these bands. which provide the ti ngerprint for the polar SIS's respectively, do not provide all the TLC evidence particular spec ies. The TL chromatograms were recorded photo­ used in this study. In Figure 4 a more detai led illustration of the graphical!) . As it is almost impossible to capture the true colours on fi ngerprints for the po lar constituents of seven of the species was the chromntograms by photographic means, it is preferable to record obtained by increasing the width of the applied band and placi ng them as colour photocopies or on a flat bed scanner. Certain species the bands closer together; the fingerprints in this Figure show contained UV active compounds: these were detected using UV light at 366 nm. how effective the technique can be. Jordaan ( 1995) proposed the re-instatement of the segregate genus Gymnosporia for the spiny Results and Discussion members of Maytenus . Five of the species studied belong to th is An analysis of the chromatograms from all four solvent systems group, namely Maytenus bachmannii ( 12), (the numbers refer to shows that the leaf extracts for each species provide a unique the TLC Tracks shown in Figures 1-4), M. heterophylla ( II ), i'v/. chemical fin gerprint that supports the specific distinctness of all mossambicensis (5), M. sp. B (4) and M. sp. C (6). The close rel a­ the species investigated. Not all the chromatograms could be tionship between these five species is evident from the chromato­ reproduced. Consequently Figures 1-3, which show representa­ grams and this is supported by the fact that they all share at least ti ve chromatograms developed in non-polar, intermediate and one major chemical constituent that distinguishes them from all

1 2 3 4 5 • 6 7 8 9 10 11 13 12 1 2 3 4 5 6 7 8 9 10 11 12 13

Figure 2 Representative TLC fin gerprints of extracts developed Figure 3 Representative TLC fi ngerprints of extracts deve loped in the SIS of intermediate po larity; light petroleum :e thyl ace­ in the the polar S/S; ethyl acetate:chloroform:formic acid (5:4: I , vi tatc:chloroform:formic acid (8:7:5. 1. v/v). v). S. A fr. J. Bot. 2000, 66( I) 9

related (see TLC tracks 7 and 8), the TLC fin gerprints for all three species were also significantly different (the TLC track for M. Iucida does not appear in any of the Figures reproduced here). M. peduncularis (I 0), a species morphologically quite differ­ ent from the other investigated taxa, is distinctive in that its extract has insufficient constituents to give a meaningful finger­ print. Our results also support the separate specific status of M abbottii (I), M. acuminata (2), AI. cordata (9) and ,\-/. sp. /1. (3 ), all of which at one stage were lumped under M. acuminata (Van Wyk 1983). TLC fingerprints of extracts from different samples of the same species from different localities showed a remarkable degree of congruency; the TLC analysis of extracts from fo ur diffe rent specimens of M. vleosa ( 13) and M. undata (7) are shown in Figure 5. Similar results were reported for Cvmhretum species coll ected from vastly different geographical locations (Carr & Rogers 1987), which helps validate this technique. 1 2 5 7 8 11 13 Although not all taxa lend themselves to TLC fingerprint­ Figure 4 Detailed li ngerprints of' seven species developed in the ing, this study shows the technique can be applied with con fi ­ polar S/S: ~.: hlororo r m : methanol :water {12 :3 :I. v/v- lower layer) . dence to the genus Maytenu.1·. Chemotaxonomic evidence thus obtained proved useful at specific and in some cases also supra­ the other members of Maytenus studied. For example see the specific levels. compound marked 'X' in Figures I and 2. Whilst this compound It must be stressed that the conclusions arrived at in this study does occur in M. undata (7), M. procumbens (8) and M. oleosa were done on many more TLC plates than those shown in Fig­ ( 13), it is obvious from their fin gerprints that these three spec ies ures 1- 5, which are not meant to represent a comprehensive are quite diffe rent from the fi ve Gymnosporia species. record of all the TLC results. Consequentl y the differences Three species, namely M acuminata (2), M. bachmannii ( 12) between certain spec ies such as M. cordata (9) and GymncJ.\poria and M. oleosa ( 13 ), contain compounds that are UV active at 366 filiform is (3 ) may not be apparent from the limited ev idence 11111. The presence of these compounds is useful to distinguish M illustrated in these Figures. oleosa ( 13 ) from the closely related and chem ically rather similar .\f undata (7). ;\-/. Iucida, a species confined to the Western References Cape, was included in the study to establish whether chemistry 13RUNING, R. & WAGNER, H. 1978. Review. Obersicht Oht:r die supports an aggregate species comprising this species, M undata Cclasraceen-inh nllsstol'l'c: chemic. chcmotaxonomie. hiosynthesc. (7 ) and M. procumbens (8) (the so-called M undata complex), or pharn1akolgie. Phytochem. 17: 182 1- 1858. three distinct taxa as currently recognised. Chemical evidence CARR, J.D. & ROGERS. C.l3. 1987. Cht:mosystcmatic studies of the clearly supports the latter view. Although chemically clearly genus Combretum (Comhretaccac ). I. A convenient method of identi­ t'ying species of this genus by a comparison or the polar constituents extracted from leaf material. S. Afi'. ./ /Jot. 53: 173-176. GONZALEZ, A.G.; JI MENEZ. I. A.: RAVELO. A. G.; SAZATORN IL & DAZZACCHI . I. L. 1993. New scsquiterpcncs with anti fecda nt activity from Maytenus canariensis (Cc lastraceae). Tetrahedron. 49: 697-702. JORDAAN. M. 1995. 1\ taxonomic rev ision of the spiny members of subfamily Celastroidcac (Ce lastraccae) in southern Africa. M.Sc. the­ sis, University of Pretoria, Pretoria. NOZAKI, H.; SUZUKI, H.; HIRAYA M/\. T.; KASAl. R.; WU. R-Y. & LEE, K-H . 1986. Antitumour tritcrpenes of Maytenus diversifo/ia. Phytochem. 25: 479-485. ROGERS, C.B. & COOM BES. P.C. 1999. Acidic tritcrpene glycosides in trichome secretions di t'tcrentiote subspecies of Comhrewm colli­ num in South Africa. Bivchem. Systematics & Ecology. 27(3): 32 1- 323. VAN WYK, A. E. 1984. A new species of Maytenus (Celastraceae) from southern Natal. S. Afr. J. Bot. 3: 11 5-11 9. VAN WYK. A.E. & ARCHER. R.H. 1987. Maytenus oleosa (Celas­ traceae), a new species from southern Natal and Pondoland. S. Afr. J. Bot. 53: 155-160. Figure 5 TLC fi ngerprints of extracts from specimens of M. VAN WYK, A.E. 1990. The sandstone regions of Natal and Pondoland: w rdata and M. oleosa collected from four different localities S/S; remarkable centres of endemism. In: Palaeoecology of Africa, cd. K. chloroform: methanol:wa ter ( 12:3: I, v/v lower layer). Heine, Vol. 2 1, pp. 243- 257. /\.A. Ba lkema. Rotterdam.