This study will investigate the effects of a potential neuroprotectant compound, YM872, in the treatment of acute ischemic stroke. The study will determine if a 24-hour infusion of YM872, given within 6 hours of stroke onset, reduces the ischemic lesion volume as measured by MRI at 28 days after the infusion is given. The clinical effects of YM872 will also be determined by neurological function and disability scores at follow up visits through Day 90 of the study.

Inclusion Criteria:

• Patients who have suffered an acute ischemic stroke and can be evaluated and treatment initiated within 6 hours after the onset of symptoms (Onset is defined as the time that which the patient was last seen in a normal state, or bedtime for unwitnessed strokes occurring during the night).
• Patients who have a three dimensionally measurable lesion compatible with an acute ischemic stroke measured using MRI.
• Patients who have a National Institutes of Health Stroke Scale (NIHSS) score of at least 7 but not more than 23 and who are conscious.
• Patients who are able to provide written informed consent or have consent provided by a legally authorized representative.
• Patients who are at least 18 years of age.
• Other criteria as specified in the study protocol

Exclusion Criteria:

• Patients who have received alteplase (t-PA) for the current stroke episode. It is assumed that all patients who are eligible will receive treatment with t-PA.
• Patients who have disability and functional limitations prior to the current stroke episode (e.g. deficit resulting from a prior stroke).
• Patients who have brain hemorrhage.
• Patients who have stroke of the brainstem or cerebellum.
• Patients who cannot be evaluated using MRI due to the presence of a pacemaker, claustrophobia, need for sedation, etc.
• Patients who have renal (kidney) disease or insufficiency.
• Patients who have active epilepsy or convulsions during the current stroke episode.
• Patients who are IV drug users or are inebriated.
• Patients who have a history of drug-related anaphylaxis.
• Patients who have taken sedatives, anticonvulsants, or any medication with sedating effects in the 10 days prior study enrollment.
• Patients who have taken more than 1.3 g of aspirin per day in the 2 days prior to enrollment.
• Patients who have a known vitamin hypersensitivity.
• Other exclusion criteria as specified by the study protocol.