Leucine is a natural product; see the link bellow for the synthesis of leucine in plants.

It is non polar. In amino acids, "polar" or "nonpolar" refers specifically to the side chain; the molecule as a whole is definitely polar, but leucine's side chain is a hydrocarbon with no polar groups.

True

Yes, HMB is the result of leucine breakdown. Leucine works to regulate blood sugar, repair muscles, and provide energy for the body.

Leucine is an essential amino acid.