It has been claimed that you cannot derive an ought from an is, or morality from reality.

I don't agree with that assessment.

If we define the highest moral value as man's life, as I believe we should, then as a result, behaving morally involves doing what is necessary to preserve that life. 

For example, gravity 'is' a reality. Therefore a person behaving morally 'ought' to wear a parachute when jumping from a plane.