The excitatory neurotransmitter L-glutamate plays a critical role in neuronal injury resulting from cerebral ischemia or head trauma, and this neuronal degeneration can be prevented by glutamate receptor antagonists or antioxidants. In our screening program for inhibitors of L-glutamate toxicity using neuronal hybridoma N18-RE-105 cells as an in vitro brain ischemia model, we previously isolated carquinostatins A, B, 4-demethoxymichigazone, lavanduquinocin, and aestivophoenins A and B. Further investigation led to the isolation of aestivophoenin C (1) from Streptomyces purpeofuscus 2887-SVS2 as a minor congener of the aestivophoenins. This paper reports the isolation, structural elucidation, and biological activities of 1. The molecular formula of 1 was determined as C29H36N2O6 by HRFAB-MS, and its structure was elucidated via NMR spectral comparison with aestivophoenin B, revealing it to be a debenzoyl derivative of aestivophoenin B. Biological assays demonstrated that 1 protected N18-RE-105 cells from L-glutamate toxicity with an EC50 value of 18.3 nM (compared to 56.3 nM for vitamin E) and also suppressed buthionine sulfoximine (BSO) toxicity with an EC50 value of 20.2 nM (versus 44.7 nM for vitamin E). Given the similarity of 1's phenazine skeleton chromophore to known antioxidants and the protective effects against oxidative stress-related toxicity, the mode of action of 1 was attributed to antioxidative activity.