Method for the synthesis of cyclic depsipeptides

1. A method of synthesizing a depsipeptide of formula (IIa) from formula (IV) and formula (III):

wherein PG2 is an amine protecting group and PG3 is a carboxylic acid protecting group, and

by:

deprotecting the amine group that is protected by PG2 in the formula (IV) in the presence of a base to obtain a deprotected amine group;

deprotecting the carboxylic acid that is protected by the group PG3 in the formula (III) in the presence of an acid to obtain a deprotected carboxylic acid group; and

condensing the deprotected amine group and the carboxylic acid group to obtain the depsipeptide of formula (IIa);

and further synthesizing a cyclic depsipeptide of formula (I) from the depsipeptide of formula (IIa):

wherein Y is an amine protecting group and X is a carboxylic acid protecting group;

wherein

R2 and R8, are independently hydrogen, straight-chain or branched C1-C8-alkyl, straight-chain or branched halogenated C1-C8 alkyl, hydroxy-C1-C6-alkyl, C1-C4-alkanoyloxy-C1-C6-alkyl, C1-C4-alkoxy-C1-C6-alkyl, aryl-C1-C4-alkyloxy-C1-C6-alkyl, mercapto-C1-C6-alkyl, C1-C4-alkylthio-C1-C6-alkyl, C1-C4-alkylsulphinyl-C1-C6-alkyl, C1-C4-alkylsulphonyl-C1-C6-alkyl, carboxy-C1-C6-alkyl, C1-C4-alkoxycarbonyl-C1-C6-alkyl, C1-C4-arylalkoxycarbonyl-C1-C6-alkyl, carbamoyl-C1-C6-alkyl, amino-C1-C6-alkyl, C1-C4-alkylamino-C1-C6-alkyl, C1-C4-dialkylamino-C1-C6-alkyl, guanidino-C1-C6-alkyl, C1-C4-alkoxycarbonylamino-C1-C6-alkyl, 9-fluorenylmethoxycarbonyl(Fmoc)amino-C1-C6-alkyl, C2-C8-alkenyl, C3-C7-cycloalkyl, C3-C7-cycloalkyl-C1-C4-alkyl, benzyl, substituted benzyl, phenyl, or phenyl-C1-C4-alkyl which may optionally be substituted by halogen;

wherein x is 1, y is 1, R1, R4, R7 and R10 are each methyl, R6 and R12 are each methyl, R5 and R11 are each independently a straight-chain or branched C1-C4-alkyl or a straight-chain or branched halogenated C1-C4-alkyl, and R3 and R9 are each independently benzyl or substituted benzyl;

wherein synthesizing a cyclic depsipeptide of formula (I) from the depsipeptide of formula (IIa) comprises:

deprotecting the amine group that is protected by Y in the presence of an acid to obtain a deprotected amine group;

deprotecting the carboxylic acid that is protected by X via hydrogenolysis to obtain a deprotected carboxylic acid group; and

condensing the deprotected amine group and the deprotected carboxylic acid group by a coupling agent to obtain the cyclic depsipeptide of formula (I),

wherein the coupling agent is BOP ((Benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate), EDCI (1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide), DEPBT (3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one), HATU (1-[Bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate), HBTU (2-(1H-benzotriazol-1-yl)-1, 1,3,3-tetramethyluronium hexafluorophosphate) or Propylphosphonic anhydride (2,4,6-Tripropyl-1,3,5,2,4,6-trioxatriphosphorinane-2,4,6-trioxide, PPACA).

2. The method of claim 1 , wherein one or both of R3 and R9 is p-morpholino substituted benzyl.

3. The method of claim 1 , wherein X is a substituted or unsubstituted —CH 2 -Aryl group.

4. The method of claim 1 , wherein X is selected from the group consisting of benzoyl (Bn), 4-methoxy-benzoyl (PMB), 3,4-dimethoxybenzoyl (DPMB), 4-phenyl-benzoyl (PPB), 2-naphthylmethyl (Nap), and Benzyloxymethyl acetal (BOM).

5. The method of claim 1 , wherein Y is t-Butyloxycarbonyl (BOC).

6. The method of claim 1 , wherein the method further comprises obtaining the formula (IV) from formula (VI) and formula (V):

wherein PG4 is an amine protecting group,

by:

deprotecting the amine group that is protected by the group PG4 in the formula (VI) in the presence of a base to obtain a deprotected amine group; and

condensing the deprotected amine group of the formula (VI) and the carboxylic acid group of the formula (V) to obtain the formula (IV).

7. The method of claim 1 , wherein the method further comprises obtaining the formula (III) from formula (VIII) and formula (VII):

wherein PG1 is an amine protecting group and PG5 is an amine protecting group,

by:

deprotecting the amine group that is protected by PG5 in the formula (VII) in the presence of a base to obtain a deprotected amine group; and

condensing the deprotected amine group of the formula (VII) and the carboxylic acid group of the formula (VIII) to obtain the formula (III).

8. The method of claim 6 , wherein the method further comprises obtaining the formula (VI) by esterifying a formula (IX) with X-LG:

wherein LG is a leaving group.

9. The method of claim 7 , wherein the method further comprises obtaining the formula (VII) by esterifying a formula (X) with PG3-OH:

10. The method of claim 9 , wherein PG3 is X.

11. The method of claim 1 , wherein the precursors of formulas (III) and (IV) are identical.

12. The method of claim 1 , wherein R3 and R9 are identical, R2 and R8 are identical, and R5 and R11 are identical.

13. The method of claim 1 , wherein the depsipeptide of formula (IIa) is selected from the group consisting of:

wherein in formulas (II-11a) to (II-14a), and (II-11b) to (II-14b) -LINK- is selected from the group consisting of:

wherein X1 can be C, N, S, or O, X2 and X3 can be C or N;

wherein X1 can be C, N, S, or O, X2, X3 and X4 can be C or N; and

wherein X1, X2, X3 and X4 can be C or N;

and wherein R13 is selected from SO 2 NH(CH 3 ), SO 2 NH 2 , OC(O)CH 3 , CF 3 or one the following lactone structures:

Y is an amine protecting group and X is a carboxylic acid protecting group;

B is an amine protecting group and A is a carboxylic acid protecting group;

PG1 is an amine protecting group and TAG is a carboxylic acid protecting group.