Can you point to someone who developed a useful medicine for 3rd-world diseases and failed to make money?

Few diseases are confined to only extremely poor areas. Medicines against malaria, for example, are a robust business. If you developed a good vaccine, you could make a lot of money selling it in Brazil, China, India, and other developing countries. The reason there is no vaccine isn't because there's no money to be made, but people have actually tried pretty hard and been unable to develop vaccines that aren't as risky as the disease itself.

The point is that most customers in the Third World are not able to afford the price point that makes such medicines profitable.

The workaround since 2000-01 or so has been differential pricing or licensing for the Third World. But this took decades to get agreements for that to happen.

Here's a good page about the situation with HIV drugs. http://www.avert.org/generic.htm

I would argue that if a medical device/drug was developed for the third-world as opposed to being a developed world hand-me-down, it would be profitable. Good book on the topic "Fortune at the bottom on the pyramid".