Process for the preparation of macrocyclic compounds
The present invention relates to a new process for the preparation of tripeptides of formula I wherein R 1 is an amino protecting group and X is a halogen atom and wherein the tipeptide contains two olefinic moieties suitably disposed to undergo an intramolecular olefin metathesis reaction and produce macrocyclic tripeptides useful for the manufacture of macrocyclic HCV protease inhibitors.
1. A process for preparing a diene of formula I wherein:
R 1 is an amino protecting group and X is a halogen atom comprising the coupling of the carboxylic acid of formula VIa or a salt thereof and the dipeptide V.
2. A process according to claim 1 wherein the coupling is carried out with a coupling agent selected from the group consisting of alkyl chloroformates, carboxylic acid halogenides and carbodiimides in the presence of a tertiary amine.
3. A process according to claim 2 wherein said coupling agent is isobutyl choroformate or pivaloyl chloride and said tertiary amine is N-methylmorpholine or triethylamine.
4. A process according to claim 1 wherein X is fluorine.
5. A process according to claim 1 which process further comprises the steps of:
(a) reacting a dipeptide of formula II wherein R 2 is an amino protecting group with carbonyl diimidazole and a compound according to formula III wherein X is a halogen and III is a free base or a salt thereof to form an N-protected carbamate of the formula IV;
(b) deprotecting the N-protected carbamate to form a compound of formula V wherein X is as above; and
(c) coupling the carbamate of formula V with the carboxylic acid of formula VIa or with a salt thereof to form the diene of formula I.
6. A process according to claim 5 wherein X is fluoride and R 1 and R 2 are a Boc protecting group.
7. A process according to claim 5 wherein said diene is a compound of formula Ib
8. A process according to claim 5 wherein step (a) is carried out in the presence of a tertiary amine base and an organic solvent.
9. A process according to claim 5 wherein the deprotection of the N-protected carbamate of formula IV in step (b) is performed with an acid in an organic solvent.