It may just be me, but he doesn't seem like the kind of guy to reinvest that money in research, considering his fraud conviction. I'd imagine he was using it to line his pockets and invest in other companies. It's not like his company developed the drug in the first place, they just bought the rights to it then marked it up massively.
Had Shkreli's sole motivation been profit, then buying the rights to daraprim would have been a moronic investment. At the time of its purchase, daraprim was an ineffective and harmful drug. Invented around 70 years ago, it inhibits the enzyme involved in causing the infection of toxoplasmosis but also inhibits a human enzyme which metabolites the vitamin B6 - quite a nasty side effect for people taking this drug daily.
Shkreli's company has since developed a new form of the drug which targets just the toxoplasma's enzyme, hence leading to no side effects. This was rather easy given modern computing and the ability to molecularly model the bug's enzyme, which wasn't possible at the time of the original drug's creation. So people who are particularly vulnerable to this bug, such as people with HIV, can take this newly developed drug in order to avoid getting toxoplasmosis in the first place, without the side effects of the original drug. I'm not sure if this new drug is in the hands of the infected at this moment in time.
So yeah, Shkreli and his company have invested both time and money into research and development projects. The evidence is out there, you just have to find it for yourself. (Lord knows the media articles you've most likely read won't share it.)
