Compounds of the following structure, wherein R.sub.1, R.sub.2, R.sub.4, R.sub.4', R.sub.6, R.sub.7, and R.sub.15 are defined above, are provided: ##STR00001## These compounds are useful in treating neurological disorders or complications due to stroke or head injury. The compounds are therefore useful as neuroprotective and neuroregenerative agents.