Optical Purity and Epimerization

Commonly Used Carbonyl Activating Reagents in Peptide Synthesis (.. . NHCH(i )C(0)-X) 

Active ester Mixed anhydride Mixed anhydride Acid azide 

To do this we knew that 3H-incorporation experiments would measure these ratios directly, with the 3H label once inserted into 17 or 19, remaining essentially inert to subsequent exchange. We had already shown for 15 (AA = Val, Asp) that the k-2/k-1 ratio was isotope 

Initial experiments by Tasker (19) were encouraging. He used 3H incorporations and RP-HPLC separations of diastereomers to show very small, and similar, 3H-incorporations and inversions (0.2-0.4%) in the synthesis of [Co(en)2((S)-Thr(Bzl)-GlyOMe)]3+ (1) and /3-[Co 

PheOMe)]3+ reagent (rather than A), a higher AA OMe concentration, and a shorter reaction time. It is likely that the Mensi and Isied result arises largely from using the racemic A,A-Co(III) reagent. 

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