b2) the compound thus obtained, of formula: ##STR18## is coupled either with a compound of formula: ##STR19## in which R2, R3 and R9 are as defined for (I) and Pr is a protecting group, for example Boc or Fmoc, then, after deprotection of the amine in acidic medium, a sulphonyl halide of formula R1 SO2 Hal in which R1 is as defined for (I) and Hal is a halogen, for example chlorine, is reacted;