**1. Introduction**

### **1.1. Iridoids**

Iridoids are considered atypical monoterpenoid compounds, based on a methylcyclopentan- [C]-pyran skeleton, often fused to a six-membered oxygen ring consisting of ten, nine or in rare cases, eight carbon atoms (Figure 1a) [1, 2]. More than 2500 iridoid compounds have been described in nature, with structural differences related mainly to the degree and type of substitution in the cyclopentane ring skeleton [3]. Iridoids can be found in nature as secoiri‐ doids (Figure 1b), a large group characterized by cleavage of the 7,8-bond on the cyclopentane ring, glycosides, mainly 1-*O*-glucosides, and nor-iridoids, originating from oxidative decar‐ boxylation on C10 or C11 (Figure 1) [3, 4]. six-membered oxygen ring consisting of ten, nine or in rare cases, eight carbon atoms (Figure 1a) [1, 2]. More than 2500 iridoid compounds have been described in nature, with structural differences related mainly to the degree and type of substitution in the cyclopentane ring skeleton [3]. Iridoids can be found in nature as secoiridoids (Figure 1b), a large group characterized by cleavage of the 7,8-bond on the cyclopentane ring, glycosides, mainly 1-*O*-glucosides, and nor-iridoids, originating from oxidative decarboxylation on C10 or C11 (Figure 1) [3, 4].

**1.1. Iridoids** 

described [20, 21].

**Figure 1.** Basic skeleton a) iridoid; b) seco-iridoid (R=H or glucose)

Iridoids are derived from isoprene units¸ which are considered the universal building blocks of all terpenoids, formed through © 2013 Amaral et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Amaral et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Figure 1. Basic skeleton a) iridoid; b) seco-iridoid (R=H or glucose)

iridoids such as aucubin and catalpol [10, 3, 11, 12].

Iridoids are derived from isoprene units¸ which are considered the universal building blocks of all terpenoids, formed through intermediates of the mevalonic acid (MVA) pathway in the citosol, and the novel 2-methyl-D-erythritol 4-phosphate (MEP) pathway in the plastids of plant cells [2, 5, 6]. The participation of two pathways in iridoid biosynthesis has not yet been clarified, but recent analyses have described the major role of the MEP in the yield of the source for the iridoid isoprene units when compared with the MVA pathway [7, 8, 9]. Iridoid biosynthesis shows two pathways, called route I and II, in which secoiridoids and carboxylated or decarboxylated iridoids are formed, respectively. Route I, considered the main pathway, is responsible for yielding the precursor of the carboxylic iridoids, from iridodial which is oxidized a iridotrial and subsequently converted to a series the iridoids, as occurs in loganin, secologanin, derived secoiridoids, and complex indole alkaloids. In route II, the presence of 8 epi-iridodial, 8-epi-iridotrial and 8-epi-deoxyloganic acid have been reported, forming a source of decarboxylated carbocyclic iridoids such as aucubin and catalpol [10, 3, 11, 12].

and *Cerbera.* According to the traditional classification, the family comprises approximately 87 iridoids, the main ones being plumieride, plumericin and isoplumericin. A review of literature comprising works published on the identification of this class of constituents within Apocy‐ naceae showed, as major natural sources, the following species (numbers in brackets indicate

A General Description of Apocynaceae Iridoids Chromatography

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(1). *Plumeria rubra* L. [*P. acuminata* W. T. Aiton; *P. acutifolia* Poir.; *P. bicolor* Ruiz & Pav.]; (2). *P. lancifolia* Müll. Arg.; (3). *P. acutifolia* Poir. [*P. rubra* L.]; (4). *P. alba* L. [*P. alba* var. *jacquiniana* A. DC.; *P. hypoleuca* Gasp.; *P. hypoleuca* var. *angustifólia* Gasp.]; (5). *P. bracteata* A. DC.; (6). *P. obtusifolia* Steud.; (7). *P. obtusa* L. [*P. multiflora* Standl.]; (8). *P. rubra* var. *alba*; (9). *P. multiflora* Standl.; (10). *Allamanda neriifolia* Hook. [*A. cathartica* var. *Schottii* (Pohl) L.H. Bailey & Raffill]; (11). *Allamanda cathartica* L. [*A. grandiflora* (Aubl.) Lam.; *A. schottii* Hook.]; (12). *Alstonia boonei* De Wild. [*A. congensis* Engl.]; (13). *Cerbera. manghas* L.; (14). *Alyxia reinwardtii* Blume; (15). *Alstonia scholaris* (L.) R.Br.; (16). *Himatanthus sucuuba* (Spruce ex Müll. Arg.) Woodson [*H. tarapotensis* (K. Schum. Ex Markgr.) Plumel; *Plumeria floribunda* Müll. Arg.; *P. tarapotensis* K. Schum. ex Markgr.]; (17). *Vinca* sp. L.; (18). *Thevetia peruviana* (Pers.) K. Schum. [*T. neriifolia* Juss. ex Steud.]; (19). *Himatanthus. phagedaenicus* (Mart.) Woodson [*Plumeria floribunda* var. *crassipes* Müll. Arg.; *P. lancifolia* var. *major* Müll. Arg.; *P. phagedaenica* Mart.]; (20). *Plumeria bicolor* Seem.; (21). *Plumeria acuminata* W.T. Aiton [*P. rubra* L.]; (22). *Cerbera odollam* Gaertn.; (23). A*llamanda. schottii* Pohl [*A. brasiliensis* Schott ex Pohl; *A. cathartica* Schrad; *A. neriifolia* Hook.]; (24). *Himatanthus articulatus* (Vahl) Woodson [*H. rigidus* Wild. Ex Roem. & Schult.; *Plumeria articulata* Vahl; *P. drastica* Mart.; *P. microcalyx* Standl.]; (25). *Rauwolfia grandiflora* Mart. Ex A. DC.; (26). *Plumeria inodora* Jacq. [*P. alba* L.; *P. alba* var. *fragrans* Kunth; *P. alba* var. *fragrantissima* G. Don; *P. alba* var. *inodora* (Jacq.) G. Don]; (27). *Himatanthus bracteatus* (A. DC.) Woodson; (28). *Himatanthus stenophyllus* Plumel; (29). *Himatanthus fallax* (Müll. Arg.) Plumel [*Plumeria fallax* Müll. Arg.]; (30). *Himatanthus obovatus* (Müll. Arg.) Woodson; (31). *Allamanda doniana* Müll. Arg.; (32). *Catharanthus roseus* (L.) G. Don; (33). *Nerium indicum* Mill. [*N. oleand‐*

*er* L.]; (34). *Alstonia macrophylla* Wall. ex G. Don; (35). *Winchia calophylla* A. DC.

allamandicin 10: *Allamanda neriifolia* 10:stem

1: *Plumeria rubra;* 10: *A. neriifolia;* 11: *A. cathartica;*

**IRIDOIDS SPECIES PLANT MATERIAL REF.**

13-*O*-acetylplumieride 10: *Allamanda neriifolia* 10:stem; 10:leaves 10: [39]; 10: [40] allamancin 10: *Allamanda neriifolia* 10:stem 10: [39]; 10: [40]

7: *Plumeria obtusa* 7:leaves 7: [37]; 7: [38]

7: *Plumeria obtusa* 7:leaves 7: [37]; 7: [38]

1:stem bark; 19,23:stem; 10,11:leaves; 11,16:root

10: [39]; 10: [41]; 10: [42]

1: [43] ; 1: [44]; 1: [48]; 1: [49]; 10: [39]; 11: [41];

species as shown in Table 1) [36]:

**1.3. Iridoids of Apocynaceae family**

6''*O*-acetylplumieride *p*-*E*coumarate

6''*O*-acetylplumieride *p*-*Z*coumarate

allamandin

Iridoids have shown a broad range of biological activities, such as an antibacterial, antifungal, anti-inflammatory, antitumoral, hepatoprotective, cardioprotective, antioxidative, antiprotozoal and anti-insect properties [13, 14, 15, 16, 17, 18, 19]. *In vitro* activities inhibiting the hepatitis C virus, the differentiation of the adipocyte, and PPARα activation activities have been also described [20, 21].

The distribution of iridoids in the Eudicotyledoneae has potential usefulness in the taxonomy of the families, related to their presence in a restricted number of families. Iridoid are considered good chemotaxonomic markers of different taxononomic groups, and can be used, in combination with order, tribe and family, to establish the phylogenetic relationship [22, 23, 10, 3, 24, 25].

According to an update of the Angiosperm Phylogeny Group (APGIII) [28,29], the presence of iridoids has been reported in approximately fifty plant families, and can be considered as one of the synapomorphies of the Asterid clade. It is divided into Lamiids, which presents iridoids of the Gentianales, Garryales and Lamiales orders, and Campanulids, which presents secoiridoids of the Asterales and Dipsacales orders. The Gentianales order comprises five families: Apocynaceae, Gelsemiaceae, Gentianaceae, Loganiaceae and Rubiaceae (APG III, 2009), highlighted for the diversity of their iridoids [11, 29, 30].
