useless, unavailing, vain
бесполезное начинание — vain undertaking
бесполезные усилия — unavailing / vain efforts
все его усилия были бесполезны — all his efforts were to no purpose, all his labour was in vain, all his efforts were wasted
бесполезная трата времени, денег и т. п. — waste of time, money, etc .