Sinningia reitzii (Hoehne) L. E. Skog (Gesneriaceae) is a subshrub native to Brazil, where it is distributed in two disjunctive populations around the 26°S and 23°S parallels. In this work, tubers of plants from the wild population growing at the 26°S parallel (Santa Catarina state) yielded two new naphthoquinones, 5,6-dihydroxy-7-methoxy-a-dunnione and 8-hydroxy-6,7-dimethoxy-a-dunnione. Three known compounds were also isolated: 6,8-dihydroxy-7-methoxy-a-dunnione, 5-hydroxy-6,7-dimethoxy-a-dunnione, and 6,8-dihydroxy-7-methoxy-2-O-methyldunniol. The naphthoquinones 6,8-dihydroxy-7-methoxy-2-O-methyldunniol, 6,8-dihydroxy-7-methoxy-a-dunnione, and 5,6-dihydroxy-7-methoxy-a-dunnione displayed antioxidant activity in the ORAC-FL method, with values of relative trolox equivalent in the range of 1.39-4.83 mmol g-1.

Phytochemical study of aerial parts from Sinningia mauroana Chautems (Gesneriaceae) yielded 17 known compounds: sitosterol, stigmasterol, betulinic acid, oleanolic acid, hederagenin, maslinic acid, ursolic acid, pomolic acid, soranjidiol, methyl 4-hydroxyphenylacetate, 6-hydroxy-7-methoxy-α-dunnione, 7-hydroxy-6-methoxy-α-dunnione, jacaranone, calceolarioside A, conandroside, luteolin, and luteolin-7-O-glucoside. Complete NMR data of 6-hydroxy-7-methoxy-α-dunnione and 7-hydroxy-6-methoxy-α-dunnione were obtained in two different solvents. Hexane, ethyl acetate and ethanol extracts were screened for antimicrobial, antioxidant and cytotoxic activities. The antimicrobial activity was assayed against Staphylococcus aureus, S. epidermidis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, C. parapsilosis, C. dubliniensis, and C. glabrata, using the microdillution method. All extracts were inactive (MIC > 100 µg mL-1). The antioxidant activity was evaluated with the ORAC method; the ethyl acetate and ethanol extracts were active (TE relative > 800 µg g-1). The cytotoxic activity was tested against PC-3 (prostate) and SKMEL-103 (melanoma) human tumor cell lines, and 3T3 fibroblast cell line, using the MTT assay. The hexane extract showed strong activity against PC-3 and SKMEL-103 human tumor cell lines (IC50 < 0.25 and 3.07 µg mL-1, respectively), and a lower activity towards 3T3 fibroblasts (IC50 = 6.84 µg mL-1). The other extracts were inactive (IC50 > 50 µg mL-1).

Chemical investigation of Sinningia warmingii (Gesneriaceae) tubers lead to the isolation of two new dimeric naphthoquinone derivatives, named warmingiins A and B, besides six known compounds, aggregatin E, aggregatin F, tectoquinone, halleridone, cleroindicin B, and cornoside. All compounds were identified by spectroscopic analysis, mainly nuclear magnetic resonance (NMR) and mass spectrometry (MS), and comparison with the literature. The structure of the warmingiin A, which is an artifact of warmingiin B, was confirmed by X-ray diffraction analysis. Antimicrobial activity of the ethanolic extract and fractions of S. warmingii was evaluated against Staphylococcus aureus, S. epidermidis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, C. dubliniensis, C. glabrata and C. parapsilosis. All samples were inactive.