“… Synthesis of tripeptide analogues 4 and 12 ; a) NaOH, (Boc) 2 O, H 2 O/ t BuOH, RT, 92 %; b) PMBCl, Et 3 N, DMF, 38 °C, 60 %; c) Na, NH 3(l) , −78 °C; d) PMBCl, −78 °C to RT, 83 % (over two steps); e) isobutyl chloroformate, Et 3 N, THF/H 2 O, 0 °C, 90 %; f) 18 or 19 , EDCI, HOBt, Et 3 N, CH 2 Cl 2 , RT, 66 % ( 20 )/46 % ( 21 ); g) TFA, anisole, reflux, RP‐HPLC 46 % ( 4 )/12 % ( 12 ); L ‐AA=δ‐( L ‐α‐aminoadipoyl). Insert: the cyclic thioether ( S )‐2‐amino‐6‐oxo‐6‐[(( S )‐2‐oxotetrahydrothiophen‐3‐yl)amino]hexanoic acid ( 22 ) was isolated as the major product from TFA‐mediated deprotection of 21 21…”