One new spirocyclic alkaloid, 5-isopentenyl-cryptoechinuline D (1), along with 11 known compounds (2-12), were isolated from a marine fungus Aspergillus ruber TX-M4-1. The structures of compounds 1-12 were elucidated by spectroscopic evidences. Compound 1 was initially isolated as an enantiomer, and further separation of 1 by chiral HPLC afforded a pair of enantiomers, including (-)-5-isopentenyl-cryptoechinuline D (1a) and (+)-5-isopentenyl-cryptoechinuline D (1b). Their absolute configurations were elucidated by ECD spectroscopic data. Compounds 1a, 5 and 10 could inhibit thioredoxin reductase (TrxR) activity with IC50 values of 6.2, 36.3 and 18.6 mu molL-1, respectively. Surface plasmon resonance (SPR) study also demonsrated the interactions between compounds 6, 8 and Niemann-Pick C1 Like 1 (NPC1L1) respectively, which indicate that compounds 6 and 8 are potential NPC1L1 inhibitors.