The most recent measurements of the observables R_{D^{(*)}} R D ( * ) are in tension with the Standard Model offering hints of New Physics in b\rightarrow c \ell \bar{\nu}_{\ell} b → c ℓ ν ‾ ℓ transitions. Motivated by these results, in this work we present an analysis on their b\rightarrow u \ell \bar{\nu}_{\ell} b → u ℓ ν ‾ ℓ counterparts (for \ell=e, ~\mu, ~\tau ℓ = e , μ , τ ). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic B B decays ( B^-\rightarrow \ell^- \bar{\nu}_{\ell} B − → ℓ − ν ‾ ℓ , \bar{B}\rightarrow \pi \ell \bar{\nu}_{\ell} B ‾ → π ℓ ν ‾ ℓ and \bar{B}\rightarrow \rho \ell \bar{\nu}_{\ell} B ‾ → ρ ℓ ν ‾ ℓ ). Here a key role is played by the leptonic B B processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel B^-\rightarrow \mu^-\bar{\nu}_{\mu} B − → μ − ν ‾ μ by the Belle collaboration. Secondly, we extract the CKM matrix element |V_{ub}| | V u b | while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic B B decays.