Activity-Guided Laboratory-Scale Process Development and Preliminary Quality Characterization of Synotis solidaginea Extract: Ethanol Extraction, Macroporous Resin Purification, Antioxidant Activity, and Safety Evaluation

This study developed an activity-guided laboratory-scale process for an extract of the aerial parts of Synotis solidaginea. Extraction conditions using 0–100% (v/v) ethanol–water solutions were screened using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays and HaCaT keratinocyte responses, followed by fractionation with AB-8 macroporous resin. The 20–50% ethanol range provided a favorable balance between antioxidant activity and cytocompatibility; 50% ethanol extraction followed by 40% ethanol elution was selected. The final dried purified S. solidaginea extract (SSE) maintained HaCaT viability above 90% at 0.01–0.2 mg/mL under the tested conditions. Under the experimental conditions evaluated, a pooled sample comprising equal masses of ten final SSE batches was classified as non-irritating in the acute eye and repeated skin irritation tests, and negative results were reported in the Ames assay and the Chinese hamster lung (CHL) cell chromosome-aberration assay. These findings are limited to the tested material and endpoints and do not establish comprehensive safety. Rutin identification was supported by liquid chromatography–tandem mass spectrometry (LC-MS/MS), and its content was determined using a preliminary high-performance liquid chromatography (HPLC) method. Reported rutin contents in ten independently prepared laboratory-scale process batches derived from a single homogenized raw-material batch ranged from 2.34% to 2.54%, with a relative standard deviation (RSD) of 2.43%. Microbiological results met the adopted limits at the time of testing. These findings support laboratory-scale process development and preliminary chemical and quality characterization of S. solidaginea extract. Further studies should evaluate independent raw-material lots, complete analytical method validation, and assess storage stability and application-specific safety.