Involved in the biosynthesis of the antimalarial endoperoxide artemisinin (PubMed:11032404, PubMed:11185551, PubMed:11289612, PubMed:10626375, PubMed:27488942). Catalyzes the formation of both olefinic and oxygenated sesquiterpenes, with amorpha-4,11-diene being the major product (PubMed:11032404, PubMed:11185551, PubMed:11289612, PubMed:10626375). (2E,6E)-farnesyl diphosphate = (+)-amorpha-4,11-diene + diphosphate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Optimum pH is 7.5-9 (PubMed:11032404). Optimum pH is 6.5-7 (at 30 degrees Celsius) (PubMed:10626375). Sesquiterpene biosynthesis. Expressed both in apical and sub-apical cells of glandular secretory trichomes. Also present in non-glandular trichome cells (PubMed:30851440). By exposure to reactive oxygen species (PubMed:11289612). Strongly induced by gibberellic acid (GA(3)) leading to an increased artemisinin yield (Ref.18). The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Artemisinin and derivatives (e.g. artesunate), are antimalarial drugs due to their endoperoxidase properties; they also display multiple pharmacological actions against inflammation,viral infections, and cell and tumor proliferation (PubMed:32514287, PubMed:32405226). Artesunate may be a promising treatment for COVID-19 mediated by the severe acute respiratory syndrome coronavirus 2 (2019-nCoV) (SARS-CoV-2) because of its anti-inflammatory activity, NF-kappaB (nuclear factor kappa B)-coronavirus effect and chloroquine-like endocytosis inhibition mechanism (PubMed:32514287, PubMed:32405226). Yeast (S.cerevisiae) has been engineered to produce artemisinic-acid, a precursor of the antimalarial artemisinin compound, by expressing AMS1/ADS, CYP71AV1, ADH1 and ALDH1 in conjunction with CYB5 and CPR1. Belongs to the terpene synthase family. Extended N-terminus.