( ±)-Dibrevianamides Q1 and Q2, the key precursors of asperginulin A from a marine-derived fungus

Two pairs of new dimeric diketopiperazine alkaloids, ( ±)-dibrevianamides Q1 and Q2 (( ±)- 1 and ( ±)- 2 ), together with seven previously reported analogues (( ±)- 3 , 4 – 6 , and ( ±)- 7 ) were obtained from a marine-derived fungus Aspergillus sp. The structures of ( ±)- 1 and ( ±)- 2 were clarified using comprehensive spectroscopic analyses, the calculated ECD, and DP4 + probability methods. Speculated from the biogenesis, ( ±)-dibrevianamides Q1 and Q2 (( ±)- 1 and ( ±)- 2 ) might be the key precursor of [2 + 2] diketopiperazine dimers (( ±)- 3 ). Compounds ( +)- 1 and ( −)- 2 displayed anti-H1N1 virus activity with IC 50 values of 12.6 and 19.5 μM. Compound ( +)- 1 showed significant activity against Mycobacterium tuberculosis (MIC, 10.2 μg/mL). Key points • Two pairs of new dimeric diketopiperazine alkaloids were obtained from the marine-derived fungus Aspergillus sp. • The structures of the new compounds were clarified using comprehensive spectroscopic analyses, the calculated ECD, and DP4 + probability methods. • ( ±)-Dibrevianamides Q1 and Q2 were speculated to be the key precursor of [2 + 2] diketopiperazine dimers ( ±)-asperginulin A. Graphical abstract