Transitional disks are structures of dust and gas around young stars with large inner cavities in which planet formation may occur. Lopsided dust distributions are observed in the dust continuum emission at millimeter wavelengths. These asymmetrical structures can be explained as being the result of an enhanced gas density vortex where the dust is trapped, potentially promoting the rapid growth to the planetesimal scale. AB Aur hosts a transitional disk with a clear horseshoe morphology which strongly suggests the presence of a dust trap. Our goal is to investigate its formation and the possible effects on the gas chemistry. We used the NOrthern Extended Millimeter Array (NOEMA) interferometer to image the 1mm continuum dust emission and the ^13^CO J=2->1, C^18^O J=2->1, SO J=5_6_->4_5_, and H_2_CO J=3_03_->2_02_. rotational lines.