Synthetics
Methyl isovalerate has a pungent, apple-like odor with a hint of bitterness.
Mosciano, Gerard P&F 15, No. 1, 19, (1990): Diffusive, sweet estery, fruity with tutti frutti nuances
Luebke, William tgsc, (1988): Strong apple fruity pineapple
Alfrebro: Strong, pungent, apple