Novel isolated DNA sequences which comprise all or part of a gene cluster encoding sanglifehrin synthase, processing and regulatory genes involved in the biosynthesis of a mixed non-ribosomal peptide/polyketide compound, or mutants having altered biosynthetic capability, polypeptides or mutants thereof encoded by DNA or the mutants, vectors containing the DNA or the mutants thereof, host cells transformed with the DNA, the mutants thereof, or the vector, and a method for producing sanglifehrin compounds. Compounds with cyclophilin inhibition activity used as immunosuppressants, antivirals or cardiac protection agents.