We isolated a new metabolite, blastmycetin D (6mg), from the mycelia (801) of Streptoverticillium blastmyceticum NA34-17, which produces Epstein-Barr virus early antigen-inducing indole alkaloids. Herein, we report the structure of blastmycetin D and its significance in teleocidin biosynthesis. Blastmycetin D is an amorphous powder with [α]D²³ -51° (c=0.27, MeOH); its molecular formula C₂₉H₄₅N₃O₃ was established by high-resolution EIMS. Its structure, elucidated via UV, IR, MS, and ¹H NMR spectra, resembles olivoretin A but includes a hydroxyl group and a distinct monoterpenoid moiety on the indole ring. Chemical conversion of blastmycetin D to olivoretin A (2) using phosphoric acid demonstrated it is a possible precursor of 2. Isotope labeling experiments with L-methionine-methyl-¹³C-methyl-d₃ showed the C-23 methyl group of teleocidin B-4 (4) derives from L-methionine, supporting the hypothesis that the C₁₁ terpenoid moiety of teleocidins forms via methylation and oxidation at C-22 of a lyngbyatoxin A-type compound, followed by intramolecular cyclization.