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A phytochemical study was performed on three native plant species from the central-western zone of Argentina: Buddleja cordobensis Grisebach, Baccharis salicina Torr. & A. Gray and Nepeta cataria L. We could obtain verbascoside (1) from B. cordobensis. From N. cataria we could obtain 1, 5, 9-epi-deoxyloganic acid (2) L. Finally, we could isolate 2--(L-rhamnopyranosyl)-3-angeloyloxy-15-acetyloxy-7,13( 14)-E-dienent-labdane (3) and 2--(L-rhamnopyranosyl)-3--angeloyloxy-15-hydroxy-7,13( 14)-E-dien-ent-labdane (4) from B. salicina. Moreover, three derivatives from 1, and one semi-synthetic derivative from 2, were prepared. PCR reaction was used to analyse the activity against DNA polymerase, and cell culture to determine cytotoxicity and antitumoral activity. Verbascoside (1) was strongly active in the nanomolar scale (IC 50 = 356 nM) against DNA polymerization. Moreover, verbascoside was also strongly active in the nanomolar scale against human melanoma cell line (IC 50 = 256 nM) and human colorectal cell line (IC 50 = 320 nM). Furthermore, derivatives 6 and 7 were cytotoxic against both cancer cell lines.