This invention discloses diterpenes class of novel compounds of general formula I from a novel source. More particularly the invention relates to extracts/fractions containing pimarane diterpenes from Anisochillus (Lamiaceae), useful for prevention, treatment, inhibition or controlling growth and proliferation of mycobacterial activity in mammals. The invention further relates to extracts, fractions standardized to diterpenes class of novel compounds useful for the treatment of cancers.