A sterically congested analog of bilirubin with propionic acid groups replaced by pivalic acids (1) was synthesized from methyl 3-(2,4-dimethyl-5-ethoxycarbonyl-lH-pyrrol-3-yl)-2-methylpropionate (8). UV-visible and NMR spectroscopic analyses of 1 suggest intramolecular hydrogen-bonding and a preference for a ridge-tile conformation. The activation parameters for MP conformational inversion of 1 were determined by dynamic NMR analysis to be ΔH‡ 19.7 ± 1.4 kcal/mole and ΔS‡ + 10.4 ± 4.5 eu. Molecular dynamics computations predict a global energy minimum for a somewhat more open ridge-tile conformation as compared with bilirubin. Circular dichroism of the pigment complex with human serum albumin gives a bisignate Cotton effect: Δε 431 max = −51, Δε 382 max = +30, with the opposite signed order as compared with that found for the parent mesobilirubin-XIIIα: and bilirubin.