A new diketopiperazine alkaloid named spirotryprostatin K (1), and five known alkaloids, spiro[5H,10H-dipyrrolo[1,2-a:1′,2′-d]pyrazine-2(3H),2′-[2H]-indole]-3′,5,10(1′H) trione (2), 6-methoxyspirotryprostatin B (3), pseurotin A (4), N-β-acetyltryptamine (5), and lumichrome (6) were isolated from the endophytic fungus Aspergillus fumigatus. The structure and the absolute configuration of spirotryprostatin K were established by extensive spectroscopic analyses, acid hydrolysis and ECD calculations. Pseurotin A exhibited indirect anti-inflammatory activity by suppressing the lipopolysaccharide-induced proinflammatory factors in BV2 microglial cells, with an IC50 of 5.20 µM.