Ocotea
Creators: name: Antonio, Ananda S.
name: Veiga-Junior, Valdir F.
name: Wiedemann, Larissa Silveira Moreira
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Laurales
Lauraceae
Ocotea

description: 2.2. Lignoids profile in Ocotea
Lignoids are the second most biosynthesized chemical class by Ocotea, which is considered the genus with third largest production of these compounds within Lauraceae (Li et al., 2018). Although their production is abundant, studies focused on the lignoids of Ocotea were mainly performed between 1983 and 2000 (Supplementary Table 2), losing attention in the scientific community due to a shift in focus to the exploitation of alkaloids. Despite the recent negligence, Ocotea lignoids can be useful and reliable tools in chemophenetics as they had already been used in a systematic approach of the genus.
One important chemophenetic statement of Lauraceae, created by Otto Gottlieb (1972), was that Ocotea species could be classified in two groups by their ability to exclusively biosynthesize either alkaloids or lignoids (Gottlieb, 1972; Maria et al., 2007). This statement was based on the observation that the phytochemical evolution would promote the specialization of the shikimate pathway to produce alkaloids instead of lignoids. Therefore, lignoids and alkaloids would not be simultaneously biosynthesized. The analytical tools available at that time for phytochemistry research, which were mainly through isolation by open column chromatography methods, contributed to the observation of only the major compounds in each extract, and for several years this theory was reaffirmed. As analytical methods were technological developed, researchers have been contradicting this statement of excluding biosynthetic pathways specialization. Although a counter-proposal has never been postulated regarding Ocotea metabolomics characterization, species such as O. macrophylla, O. duckei and O. minarum have been reported as accumulators of both alkaloids and lignoids after the year 2000 (Barbosa-Filho et al., 2008; Coy-Barrera et al., 2009; Garcez et al., 2005).
Lignoids are mainly found within the branches and roots of Ocotea species. Only 15 different species of Ocotea had any level of description of their lignoid content. Within these species, literature data show 124 distinct compounds, classified as lignans, epoxylignans, diepoxylignans, neolignans, cycloneolignans and oxyneolignans (Supplementary Table 2). O. catharinensis can be highlighted as the greatest biosynthesizer of cycloneolignans, with an occurrence number of 44, which is 14 times bigger than the average of the other species (Supplementary Table 3). The chemodiversity within this structural class could be further applied in metabolomics to specifically characterize this species within the genus. Cycloneolignans distinct occurrence in O. catharinensis acts as an outlier during multivariate analysis, causing loss of resolution in the formation of clusters. Therefore, this species was removed during HCPC analysis to enable a better visualization of the clustering formation of the remaining species.
HCPC analysis of the occurrence number of lignoids of the mentioned structural classes (data in Supplementary Table 3) indicates the formation of 5 clusters with an explained variance of 77.45% (Fig. 4). Ocotea duckei is the only species that comprises Cluster 1, which is due to the presence of 7 different diepoxylignans, including one of its most popular biomarkers, yangambin (Barbosa-Filho et al., 2008). Besides O. duckei, only O. heterochroma has previously been described with diepoxylignans in its chemical composition (Cuca et al., 2009; Li et al., 2018). This result demonstrates that not only can yangambin efficiently be used as biomarker but also the other diepoxylignans. As diepoxylignans are exclusively produced by O. duckei within Ocotea, this chemical class could be used as a species-specific biomarker within the genus, considering the current knowledge of the genus chemistry.
Cluster 2 is characterized by species with large occurrence of neolignans, such as O. aciphylla and O. cymosa. O. porosa alone is a new cluster (Cluster 3), with a low Euclidian distance to Cluster 2. It is distinct due to its occurrence number of cycloneolignans, indicating the ability of this structural class to act as specific biomarkers in untargeted approaches to differentiate Ocotea species.
Cluster 4 is also characterized by the presence of cycloneolignans, though with lower diversity than Cluster 1. Moreover, Cluster 5 (Fig. 4) was the least resolved since it was formed by species with the lowest occurrence number of lignoids (Supplementary Table 3). The low resolution may occur due to few researchers investigating this cluster species and also that the main focus of those studies is the isolation of bioactive compounds.
Essentially, HCPC analysis (Fig. 4) classified species in terms of the specialization of the lignoid biosynthetic pathways, in which clusters were characterized by species production of neolignans, diepoxylignans and cycloneolignans. Clustering patterns demonstrated the connection of O. duckei, O. aciphyla, O. porosa and O. cymosa to more specialized biosynthetic pathways, as they possess compounds with the highest levels of oxidation, and therefore can be considered newer species in the evolutionary lineage of Ocotea. Further development regarding the metabolomic profile and phylogenetic characterization of these species is still required to confirm their position in a non-basal group of Ocotea.
Among the Ocotea lignoids, 13.2% are classified as lignans, of which cymosalignans and yangambim (Fig. 5) present a high relevance in species identification though metabolomics as they have only been found in 3 species of Lauraceae. The separation of O. cymosa (Cluster 2) during HCPC analysis could be related to cymosalignan, as this is the only species where it can be found, proving its reliability as a specific biomarker for targeted and untargeted metabolomic classification systems. As yet, yangambin has only been described in three species of Lauraceae (O. duckei, Cinnamomum cassia and O. heterochroma) (Barbosa-Filho et al., 2008; Cuca et al., 2009; Liu et al., 2018), therefore, it can be readily applied in the construction of targeted and untargeted metabolomic models for O. duckei specific identification and differentiation.
Among Ocotea neolignans, 52.0% were bicyclo [3.2.1]octaneneolignans, in which ferrearin, burchelin, armenine and canelline (Fig. 5) presented the highest occurrence numbers. As these neolignans are easily found in other species of the Ocotea complex (David et al., 1994; Chanderbali et al., 2001; Funasaki et al., 2009; Li et al., 2018), their usage as biomarkers is not recommended for both, targeted and untargeted approaches. On the other hand, ocobullenone and eusiderin had a high significance in an untargeted metabolomic approach for identification and classification proposes as they were described in only 10 species of the Ocotea complex (Teponno et al., 2016; Li et al., 2018), including Ocotea species itself. Therefore, they can be specific markers for a small subset of species.
The application of lignoids in systematics is more feasible for untargeted approaches and multifactorial models, as few compounds of this class are exclusive for Ocotea or the Ocotea complex. Additionally, the application of this chemical class requires the analysis of more species, since only 3.7% of Ocotea species have any description of their lignoid profile.
description: Published as part of Antonio, Ananda S., Veiga-Junior, Valdir F. & Wiedemann, Larissa Silveira Moreira, 2020, Ocotea complex: A metabolomic analysis of a Lauraceae genus, pp. 1-8 in Phytochemistry (112314) (112314) 173 on pages 4-5, DOI: 10.1016/j.phytochem.2020.112314, http://zenodo.org/record/8294527