Structure elucidation of 11-amino-8-hydroxypentacyclo[5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane-8,11-lactam through selective acetylation and complete 1H and 13C NMR spectral assignment of the mono-, di- and triacetates

NMR techniques cannot unambiguously distinguish between 11-amino-8-hydroxypentacyclo[5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane-8,11-lactam and 8-amino-11-hydroxypentacyclo[5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane-8,11-lactam, both of which are possible products during the reaction of pentacyclo[5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane-8,11-dione with Strecker reagents. Treatment of 11-amino-8-hydroxy-pentacyclo[5.4.0.0(2, 6).0(3, 10).0(5, 9)]undecane-8,11-lactam with acetic anhydride at room temperature produced a monoacetate. With acetic anhydride containing sodium acetate, a triacetate was obtained at reflux temperature. Treatment with acetyl chloride and N,N-dimethylaniline produced a diacetate. High-field 1H and 13C NMR techniques were used in the structure elucidation and assignment of the different NMR resonances of these three acetylated compounds.     

Phytochemical Profiling and Quality Control of Terminalia sericea Burch. ex DC. Using HPTLC Metabolomics

Terminalia sericea is used throughout Africa for the treatment of a variety of conditions and has been identified as a potential commercial plant. The study was aimed at establishing a high-performance thin layer chromatography (HPTLC) chemical fingerprint for T. sericea root bark as a reference for quality control and exploring chemical variation within the species using HPTLC metabo3lomics. Forty-two root bark samples were collected from ten populations in South Africa and extracted with dichloromethane: methanol (1:1). An HPTLC method was optimized to resolve the major compounds from other sample components. Dichloromethane: ethyl acetate: methanol: formic acid (90:10:30:1) was used as the developing solvent and the plates were visualized using 10% sulfuric acid in methanol as derivatizing agent. The concentrations of three major bioactive compounds, sericic acid, sericoside and resveratrol-3-O-β-rutinoside, in the extracts were determined using a validated ultra-performance liquid chromatography-photodiode array (UPLC-PDA) detection method. The rTLC software (written in the R-programming language) was used to select the most informative retardation factor (Rf) ranges from the images of the analysed sample extracts. Further chemometric models, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), were constructed using the web-based high throughput metabolomic software. The rTLC chemometric models were compared with the models previously obtained from ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS). A characteristic fingerprint containing clear bands for the three bioactive compounds was established. All three bioactive compounds were present in all the samples, although their corresponding band intensities varied. The intensities correlated with the UPLC-PDA results, in that samples containing a high concentration of a particular compound, displayed a more intense band. Chemometric analysis using HCA revealed two chemotypes, and the subsequent construction of a loadings plot indicated that sericic acid and sericoside were responsible for the chemotypic variation; with sericoside concentrated in Chemotype 1, while sericic acid was more abundant in Chemotype 2. A characteristic chemical fingerprint with clearly distinguishable features was established for T. sericea root bark that can be used for species authentication, and to select samples with high concentrations of a particular marker compound(s). Different chemotypes, potentially differing in their therapeutic potency towards a particular target, could be distinguished. The models revealed the three analytes as biomarkers, corresponding to results reported for UPLC-MS profiling and thereby indicating that HPTLC is a suitable technique for the quality control of T. sericea root bark.