Sesquiterpene cyclase; part of the gene cluster that mediates the biosynthesis of astellolides, drimane-type sesquiterpene esters that show antimicrobial, anti-inflammatory, and anti-tumor activities (PubMed:27628599). The first step in astellolide biosynthesis is performed by the sesquiterpene cyclase astC that catalyzes the formation of drimanyl pyrophosphate from farnesyl pyrophosphate (PubMed:27628599). Drimanyl pyrophosphate is then dephosphorylated by the sesquiterpene phosphatase astI to produce drimanyl monophosphate which is further dephosphorylated to drim-8-ene-11-ol by atsK (PubMed:27628599). Drim-8-ene-11-ol is converted to confertifolin, probably by the cytochrome P450 monooxygenase astD and/or the dehydrogenase astE (PubMed:27628599). The cytochrome P450 monooxygenases astB, astF and astJ then hydroxylate confertifolin at C6, C14, or C15 to form trihydroxy confertifolin (PubMed:27628599). The nonribosomal peptide synthetase astA catalyzes ester bond formation between trihydroxy contifolin and benzoic acid (BA) or 4-hydroxy benzoic acid (4HBA), leading to the formation of dideacetyl astellolides A and B, respectively (PubMed:27628599). Finally, the O-acetyltransferase astG converts dideacetyl astellolides A and B into deacetyl astellolides A and B (PubMed:27628599). Secondary metabolite biosynthesis; terpenoid biosynthesis. Expression is regulated by the secondary metabolite regulator cclA. Belongs to the HAD-like hydrolase superfamily.