You can escape parentheses with a backslash, like so:
[Wiki link](http://en.wikipedia.org/wiki/List\_of\_countries\_by\_GDP\_\\(PPP\\\)\_per\_capita)
producing:
Wiki link_per_capita)
(You also need to escape underscores if you want to avoid toggling italics in body text, but it’s not an issue in the destination field of links.)
You can escape parentheses with a backslash, like so:
[Wiki link](http://en.wikipedia.org/wiki/List\_of\_countries\_by\_GDP\_\\(PPP\\\)\_per\_capita)
producing:
Wiki link_per_capita)
(You also need to escape underscores if you want to avoid toggling italics in body text, but it’s not an issue in the destination field of links.)