No, such a possibility does not exist.
Up to CS6 a serial is limited to language and OS. Cross grades were possible in the time, until the next version came. After the next version was announced only updates were possible.
CS5 is quite old, since then was C5.5, CS6, CC and CC 2014, only to name the main upgrades. Now you can only subscribe to the Creative Cloud.
A CS 5 license is still upgradeable to CS6. To go from Windows to Mac
would require a call to Adobe to get a cross platform upgrade.
Other possibility is to run Windows on the Mac.