Complex sentence: As the solution is converted to a mixture of sucrose, fructose and glucose, the amount of rotation is reduced until (in a fully converted solution) the direction of rotation has changed (inverted) from right to left.
Split into simpler sentences: As the solution is converted to a mixture of sucrose, fructose and glucose, the amount of rotation is reduced. In the fully converted solution the direction of rotation has changed (inverted) from right to left.