In a first step, eight ACLs were screened for activity towards 12 aliphatic-, phenyl substituted-, mono-and di-carboxylic acids (1b-12b, Figure ). These thermophilic enzymes were selected based on previous results (Table ). The screening was conducted in the presence of slight excess of AMFC as nucleophilic amine in MOPS buffer at pH 8 at the temperature of 60 °C to promote the spontaneous nucleophilic aminolyse of the adenylate intermediate (Scheme 2).