1. On-line structure characterization of pyrrolizidine alkaloids in Onosma stellulatum and Emilia coccinea by liquid chromatography-ion-trap mass spectrometry
Karine Ndjoko, Kazimierz Głowniak, Tomasz Mroczek, Kurt Hostettmann J Chromatogr A . 2004 Nov 12;1056(1-2):91-7.
On-line structure characterization of pyrrolizidine alkaloids in two various plant species (Onosma stellulatum W.K., family Boraginaceae and Emilia coccinea Sims., family Compositae) was performed by a newly elaborated RP-HPLC ion trap MS method with atmospheric pressure chemical ionization (APCI) interface. Different PAs (N-oxides, free bases, otonecine alkaloids) isolated were separated on Waters XTerra C18 column using a gradient elution. The combination of a CE-SPE with multiple isolation and fragmentation steps for specific masses in ion trap MS detector enabled fast and sensitive analysis of various types of PAs (N-oxides and free bases). In O. stellulatum, spectra 12 various types of structures (13 different alkaloids) have been determined for the first time: leptanthine-N-oxide, lycopsamine-N-oxide, heliospathuline, lycopsamine, trachelanthamine-N-oxide, dihydroechinatine, leptanthine, heliospathuline-N-oxide, 7-acetylintermedine, uplandicine, echimidine and echimidine-N-oxide. In E. coccinea, the following types of PAs were found: platyphylline-N-oxide, platyphylline (three stereoisomers with the same MS(n) spectrum), ligularidine, neoligularidine, neosenkirkine and also previously reported senkirkine. The method elaborated can be applied in the structural analysis of PAs in newly examined plant materials or food products but further analysis is needed to determine the stereochemistry in details.
2. Tissue distribution, core biosynthesis and diversification of pyrrolizidine alkaloids of the lycopsamine type in three Boraginaceae species
Thomas Hartmann, Dietrich Ober, Cordula Frölich Phytochemistry . 2007 Apr;68(7):1026-37. doi: 10.1016/j.phytochem.2007.01.002.
Three species of the Boraginaceae were studied: greenhouse-grown plants of Heliotropium indicum and Agrobacterium rhizogenes transformed roots cultures (hairy roots) of Cynoglossum officinale and Symphytum officinale. The species-specific pyrrolizidine alkaloid (PA) profiles of the three systems were established by GC-MS. All PAs are genuinely present as N-oxides. In H. indicum the tissue-specific PA distribution revealed the presence of PAs in all tissues with the highest levels in the inflorescences which in a flowering plant may account for more than 70% of total plant alkaloid. The sites of PA biosynthesis vary among species. In H. indicum PAs are synthesized in the shoot but not roots whereas they are only made in shoots for C. officinale and in roots of S. officinale. Classical tracer studies with radioactively labelled precursor amines (e.g., putrescine, spermidine and homospermidine) and various necine bases (trachelanthamidine, supinidine, retronecine, heliotridine) and potential ester alkaloid intermediates (e.g., trachelanthamine, supinine) were performed to evaluate the biosynthetic sequences. It was relevant to perform these comparative studies since the key enzyme of the core pathway, homospermidine synthase, evolved independently in the Boraginaceae and, for instance, in the Asteraceae [Reimann, A., Nurhayati, N., Backenkohler, A., Ober, D., 2004. Repeated evolution of the pyrrolizidine alkaloid-mediated defense system in separate angiosperm lineages. Plant Cell 16, 2772-2784.]. These studies showed that the core pathway for the formation of trachelanthamidine from putrescine and spermidine via homospermidine is common to the pathway in Senecio ssp. (Asteraceae). In both pathways homospermidine is further processed by a beta-hydroxyethylhydrazine sensitive diamine oxidase. Further steps of PA biosynthesis starting with trachelanthamidine as common precursor occur in two successive stages. Firstly, the necine bases are structurally modified and either before or after this modification are converted into their O(9)-esters by esterification with one of the stereoisomers of 2,3-dihydroxy-2-isopropylbutyric acid, the unique necic acid of PAs of the lycopsamine type. Secondly, the necine O(9)-esters may be further diversified by O(7)- and/or O(3')-acylation.
3. Rinderidine and oblongifolidine new pyrrolizidine alkaloids from Rindera oblongifolia M. Popov and their absolute configurations
B Tashkhodzhaev, R Ya Okmanov, N I Mukarramov, Kh M Bobakulov, R M Ruzibaeva, N D Abdullaev, A M Nigmatullaev Nat Prod Res . 2022 Oct 18;1-11. doi: 10.1080/14786419.2022.2134865.
The alkaloid composition ofRindera oblongifoliawas studied, in which the pyrrolizidine alkaloids echinatine and trachelanthamine N-oxide, as well as two new quaternary salts namely rinderidine and the oblongifolidine were isolated. The structures of the isolated new alkaloids were elucidated by NMR spectroscopy. The absolute configuration of lindelofine, trachelanthamine N-oxide, rinderidine and oblongifolidine was established by single crystal X-ray diffraction as: 1R, 4R, 8R, 2'S, 3'R; 1R, 4S, 8S, 2'S, 3'R; 4R, 7S, 8R, 2'S, 3'S; 4R, 7S, 8R, 2'S, 3'S(7''S, 8''R) respectively. Both new pyrrolizidine alkaloids showed no cytotoxicity against four cancer cell lines such as HeLa, НEр-2, HBL-100 and CCRF-CEM.