Oxazolones are known to racemise. The synthetic chemistry used to make formylaminoacyl mixed anhydrides in this work would likely produce 5-(4H)oxazolones as reactive intermediates, so we would expect both diastereoisomers of the formylaminoacyl mixed anhydrides to be formed. Stereoselectivity of transfer of (Nacyl)-aminoacyl residues would have been important to nascent translation to ensure diasteromerically pure proteins. We and others have previously demonstrated that the transfer of aminoacyl residues from a mixed anhydride in a nicked loop 14 or nicked duplex configuration is stereoselective (with some exceptions for specific sequences 15 ). However, nicked loop transfer of AcAla residues is not stereospecific. 14 This last observation is interesting in comparison to a previous report that AcAla residues do infact transfer stereoselectively in a nicked duplex. As diastereoselectivity of transfer had only been studied for the transfer of AcAla residues, we studied the transfer of the more prebiotically plausible fAla residues used in this work. A 5-mer mixed anhydride synthesised from L-fAla as a donor strand was mixed was mixed with a 10-mer acceptor strand (1 eq. 5'-fAla-pAGCGA mixed anhydride with 1 eq. 5'-UCGCUUUCCA forming a nicked loop) or with a 10-mer template strand and 8-mer acceptor strand (1 eq. 5'-fAla-pAGCGA mixed anhydride with 1 eq. 5'-UCGCUUUCCA template and 1 eq. 5'-UAAUGGAA acceptor making a nicked duplex). fAla transfer to their acceptors was identified in (Fig S16 ) across a nicked loop or (Fig S17 ) nicked duplex respectively by the presence of new peaks with increased retention time consistent with our previous experiments. The crude mixtures were digested by RNAse A as before and analysed by HPLC (Fig. ).