All CNS diseases have the big problem of BBB - this limits the number of molecules that can really treat CNS - as such all pharma stick to same molecule once they find that it can overcome BBB and then comes non- toxicity and then comes efficacy.
A2-73 has crossed the BBB hurdle and toxicity which is big news - now we are looking at efficacy. If 3-71 proves that it can cross BBB hurdle - AVXL will have 2 potent compounds on hand and right scientific minds can do some wonders - so I personally think the risk-reward in this case is highly tilted to rewards (all biotechs have high risk until proven successful)
"Summary: The blood-brain barrier (BBB) is formed by the brain capillary endothelium and excludes from the brain ~100% of large-molecule neurotherapeutics and more than 98% of all small-molecule drugs. Despite the importance of the BBB to the neurotherapeutics mission, the BBB receives insufficient attention in either academic neuroscience or industry programs. ..."