Airspeed isn't directly related to AoA - rather, it is related to total drag, which in turn is related to AoA. So yes, AoA does affect airspeed but not in a very direct sense. So, an equation? The best relationship I can think of at the moment is the very obvious restatement of what I just said - 'airspeed is inversely proportional to AoA' (as AoA increases, drag increases and as a result airspeed decreases).
To conjure up a 'raw' equation, one would most likely need a graph of AoA versus CL for the particular airfoil involved, to obtain a value for CL which could then be plugged into the equation for induced drag, the main contributor to changes in drag from changes in AoA. You would then need to set up a thrust-required graph and somehow derive a workable equation from all of that. This is beyond me, but someone else may be able to find a feasible equation for you. Or, better yet, there may be a pilot out there who has a handy rule of thumb regarding airspeed versus AoA.
Sorry I couldn't be of more help!