Targeted isolation of antitubercular cycloheptapeptides and an unusual pyrroloindoline-containing new analog,asperpyrroindotide A,using LC–MS/MS-based molecular networking

Further insights on the secondary metabolites of a soft coral-derived fungus Aspergillus versicolor under the guidance of MS/MS-based molecular networking led to the isolation of seven known cycloheptapeptides,namely,asperversiamides A–C(1–3)and asperheptatides A–D(4–7)and an unusual pyrroloindoline-containing new cycloheptapeptide,asperpyrroindotide A(8).The structure of 8 was elucidated by comprehensive spectroscopic data analysis,and its absolute configuration was determined by advanced Marfey’s method.The semisynthetic transformation of 1 into 8 was successfully achieved and the reaction conditions were optimized.Additionally,a series of new derivatives(10−19)of asperversiamide A(1)was semi-synthesized and their anti-tubercular activities were evaluated against Mycobacterium tuberculosis H37Ra.The preliminary structure−activity relationships revealed that the serine hydroxy groups and the tryptophan residue are important to the activity.