TLC and HPTLC-APCI-MS for the rapid discrimination of plant resins frequently used for lacquers and varnishes by artists and conservators.

INTRODUCTION: Depending on their terpenoid and phenolic constituents plant resins can be classified as diterpenoid, triterpenoid or phenolic resins; thereby the profile of diterpenes and triterpenes is considered as genus- or even species-specific. OBJECTIVES: We aimed to develop a simple, rapid, inexpensive, sensitive and specific method for the identification of resin-specific triterpenoid and phenolic compounds in plant resins using (HP)TLC [(high-performance) thin-layer chromatography] combined with APCI-MS (atmospheric pressure chemical ionisation mass spectrometry) and post-chromatographic detection reactions. METHODS: Twenty resin samples from different plant species were analysed. Different extraction procedures, post-chromatographic detection reagents as well as various sorbents and solvents for planar chromatography were tested. To evaluate the potential of the optimised (HP)TLC-APCI-MS methods, parameter such as limit of detection (LOD) was determined for selected marker compounds. RESULTS: Our protocol enabled qualitative analyses of chemotaxonomic molecular markers in natural resins such as dammar, mastic, olibanum and benzoin. For the first time, the application of thionyl chloride-stannic chloride reagent for a specific post-chromatographic detection of triterpenes is reported, sometimes even allowing discrimination between isomers based on their characteristic colour sequences. For triterpene acids, triterpene alcohols and phenolic compounds, detection limits of 2-20 ng/TLC zone and a system precision with a relative standard deviation (RSD) in the range of 3.9%-7.0% were achieved by (HP)TLC-APCI-MS. The applicability of the method for the analysis of resin-based varnishes was successfully tested on a mastic-based varnish. Thus, the method we propose is a helpful tool for the discrimination of resins and resin-based varnishes with respect to their botanical origin.

Degumming and characterization of Bombyx mori and non-mulberry silks from Saturniidae silkworms.

In this study, cocoons and degummed silk samples of Bombyx mori and twenty Saturniidae species of the genera Actias, Attacus, Argema, Antheraea, Caligula, Callosamia, Cricula, Epiphora, Hyalophora, Loepa, Samia and Saturnia are studied to gain an insight into their morphology, chemical composition and physical structure. For this purpose, silk samples are characterized by optical microscopy and FTIR spectroscopy in attenuated total reflection mode (ATR-FTIR spectroscopy). Furthermore, degummed silk samples are analyzed for their amino acid (AA) composition by GC-FID. In the course of method development, various degumming methods are tested using alkalis, citric acid, enzymes and detergents. A mixture of 0.1% sodium carbonate and 2.5% ethylenediamine proves to be an effective agent for degumming Saturniidae and B. mori cocoons. After hydrolysis of the fibroin filaments with 6 N hydrochloric acid and derivatization with propyl chloroformate, fifteen AAs are identified and qualified. This method shows a satisfactory overall analytical performance with an average recovery rate of 95% at the medium concentration level. The chemical composition of the different silks was considered comparatively. Within a genus, the analyses usually show a high degree of similarity in AA composition and the resulting structural indices, whereas differences are found between genera.

Natural abenquines and synthetic analogues: Preliminary exploration of their cytotoxic activity.

In this study, we explore the cytotoxic activity of four natural abenquines (2a-d) and fourteen synthetic analogues (2e-j and 3a-h) against a panel of six human cancer cell lines using a SRB assay. It was found that most of the compounds revealed higher levels of cytotoxic activities than naturally occurring abenquines. The analogues carrying ethylpyrrolidinyl and ethylpyrimidinyl with either an acetyl group (2h-i) or a benzoyl group (3f-g), were the most potent against all human cancer cell lines and displayed EC50 between a range of 0.6-3.4µM. Notably, of the compounds tested, compound 2i proved the most cytotoxic against both ovarian (A2780) and breast (MCF7) cells, showing EC50=0.6 and 0.8µM respectively. Likewise, the analogues 2i, 3f and 3g showed strong activity against cell HT29 with EC50=0.9µM for these compounds.

Rhodamine B conjugates of triterpenoic acids are cytotoxic mitocans even at nanomolar concentrations.

Triterpenoic acids 1-6 exhibited very low or no cytotoxicity at all, but their corresponding 2,3-di-O-acetyl-piperazinyl amides 13-18 showed low EC50 values for several human tumor cell lines. Their cytotoxicity, however, was also high for the non-malignant mouse fibroblasts NIH 3T3. A significant improvement was achieved by preparing the rhodamine B derivatives 19-24. While rhodamine B is not cytotoxic (up to a concentration of 30µM - cut-off of the assay), the triterpenoid piperazine-spacered rhodamine B derivatives were cytotoxic in nano-molar concentration. Compound 24 (a diacetylated maslinic acid derivative) was most toxic for several human tumor cell lines but less toxic for mouse fibroblasts NIH 3T3. Staining and double-staining experiments revealed 24 to act as a mitocan.