Pyrrolobenzodiazepines as key intermediates in the synthesis of dimeric cytotoxic pyrrolobenzodiazepines

1. A compound of formula Ia or Ib:

or a pharmaceutically acceptable salt thereof, wherein:

the dotted lines indicate the optional presence of a double bond between C1 and C2 or C2 and C3;

R 2 and R 3 are independently selected from —H, ═O, ═CH 2 , —CN, —R, OR, halo, ═CH—R, O—SO 2 —R, CO 2 R and COR;

R 6 and R 9 are independently selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo;

where R and R′ are independently selected from optionally substituted C 1-12 alkyl, heterocyclyl groups having 3 to 20 ring atoms of which 1 to 10 are heteroatoms independently selected from the group consisting of N, O and S and aryl or heteroaryl groups having 5 to 20 ring atoms, the heteroaryl groups having one or more heteroatoms independently selected from the group consisting of N, O and S, wherein the optional substituents are independently selected from halo, hydroxy, ether, alkoxy, acetal, hemiacetal, ketal, hemiketal, oxo, thione, imino, formyl, acyl, carboxy, thiocarboxy, thiolcarboxy, thionocarboxy, imidic acid, hydroxamic acid, ester, acyloxy, oxycaroyloxy, amino, amido, thioamido, acylamido, aminocaronyloxy, ureido, guanidino, tetrazolyl, amidino, nitro, nitroso, azido, cyano, isocyano, cyanato, isocyanato, thiocyano, isothiocyano, sulfhydryl, disulfide, sulfine, sulfonyl, sulfino, sulfo, sulfinate, sulfonate, sulfinyloxy, sulfonyloxy, sulfate, sulfamyl, sulfonamido, sulfamino, sulfonamino, sulfinamino, phosphino, phosphor, phosphinyl, phosphono, phosphonate, phosphonooxy, phosphate, phosphorous acid, phosphite, phosphoramidite, or phosphoramidate;

R A is selected from H, R, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo;

R 10 is a carbamate-based nitrogen protecting group; and

R 11 is an oxygen protecting group.

2. A compound according to claim 1 , wherein R A is independently selected from H, OR, SH, SR, NH 2 , NHR, NRR′ and halo.

3. A compound according to claim 1 , wherein R 11 is THP or a silyl oxygen protecting group.

4. A compound according to claim 1 , wherein R 10 is BOC or Troc.

5. A compound according to claim 1 , wherein R 9 is H.

6. A compound according to claim 1 , wherein R 2 is R.

7. A compound according to claim 1 , wherein R 6 is selected from H, OH, OR, SH, NH 2 , nitro and halo.

8. A method of synthesizing a compound of formula Ia or Ib:

from a compound of formula IIa or IIb respectively:

comprising deprotecting a C7 or C8 hydroxyl moiety, wherein:

the dotted lines indicates the optional presence of a double bond between C1 and C2 or C2 and C3;

R 2 and R 3 are independently selected from —H, ═O, ═CH 2 , —CN, —R, OR, halo, ═CH—R, O—SO 2 —R, CO 2 R and COR;

R 6 and R 9 are independently selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo;

where R and R′ are independently selected from optionally substituted C 1-12 alkyl, heterocyclyl groups having 3 to 20 ring atoms of which 1 to 10 are heteroatoms independently selected from the group consisting of N, O and S and aryl or heteroaryl groups having 5 to 20 ring atoms, the heteroaryl groups having one or more heteroatoms independently selected from the group consisting of N, O and S, wherein the optional substituents are independently selected from halo, hydroxy, ether, alkoxy, acetal, hemiacetal, ketal, hemiketal, oxo, thione, imino, formyl, acyl, carboxy, thiocarboxy, thiolcarboxy, thionocarboxy, imidic acid, hydroxamic acid, ester, acyloxy, oxycaroyloxy, amino, amido, thioamido, acylamido, aminocaronyloxy, ureido, guanidino, tetrazolyl, amidino, nitro, nitroso, azido, cyano, isocyano, cyanato, isocyanato, thiocyano, isothiocyano, sulfhydryl, disulfide, sulfine, sulfonyl, sulfino, sulfo, sulfinate, sulfonate, sulfinyloxy, sulfonyloxy, sulfate, sulfamyl, sulfonamido, sulfamino, sulfonamino, sulfinamino, phosphino, phosphor, phosphinyl, phosphono, phosphonate, phosphonooxy, phosphate, phosphorous acid, phosphite, phosphoramidite, or phosphoramidate;

R A is selected from H, R, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo;

R 10 is a carbamate-based nitrogen protecting group;

R 11 is an oxygen protecting group; and

R 14 is an oxygen protecting group orthogonal to R 11 .

9. A method according to claim 8 , wherein R 14 is benzyl ether and R A is OMe or H.

10. A method according to claim 8 , wherein R 11 is THP or a silyl oxygen protecting group.

11. A method of synthesising a compound of formula IIIa or IIIb:

from a compound of formula Ia or Ib respectively:

wherein:

the dotted lines indicate the optional presence of a double bond between C1 and C2 or C2 and C3;

R 2 and R 3 are independently selected from —H, ═O, ═CH 2 , —CN, —R, OR, halo, ═CH—R, O—SO 2 —R, CO 2 R and COR;

R 6 , R 9 , R 12 and R 13 are independently selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo; where R and R′ are independently selected from optionally substituted C 1-12 alkyl, heterocyclyl groups having 3 to 20 ring atoms of which 1 to 10 are heteroatoms independently selected from the group consisting of N, O and S and aryl or heteroaryl groups having 5 to 20 ring atoms, the heteroaryl groups having one or more heteroatoms independently selected from the group consisting of N, O and S, wherein the optional substituents are independently selected from halo, hydroxy, ether, alkoxy, acetal, hemiacetal, ketal, hemiketal, oxo, thione, imino, formyl, acyl, carboxy, thiocarboxy, thiolcarboxy, thionocarboxy, imidic acid, hydroxamic acid, ester, acyloxy, oxycaroyloxy, amino, amido, thioamido, acylamido, aminocaronyloxy, ureido, guanidino, tetrazolyl, amidino, nitro, nitroso, azido, cyano, isocyano, cyanato, isocyanato, thiocyano, isothiocyano, sulfhydryl, disulfide, sulfine, sulfonyl, sulfino, sulfo, sulfinate, sulfonate, sulfinyloxy, sulfonyloxy, sulfate, sulfamyl, sulfonamido, sulfamino, sulfonamino, sulfinamino, phosphino, phosphor, phosphinyl, phosphono, phosphonate, phosphonooxy, phosphate, phosphorous acid, phosphite, phosphoramidite, or phosphoramidate;

R A is selected from H, R, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo;

R 10 is a carbamate-based nitrogen protecting group and R 15 is either O—R 11 , wherein R 11 is an oxygen protecting group, or OH, or R 10 and R 15 together form a double bond between N10 and C11; and

where R″is a C 3-12 alkylene group, and each X is O; and R 2′ , R 3′ , R 6′ , R 9′ , R 10′ , R 12′ , R 13′ and R 15′ are all independently selected from the same lists as previously defined for R 2 , R 3 , R 6 , R 9 , R 10 , R 12 , R 13 and R 15 respectively, comprising either:

(a) reacting a compound of formula Ia or Ib with a compound having the formula Y—R″—Y′ to yield a compound of formula IIIa or IIIb; or

(b) (i) reacting a compound of formula Ia or Ib with a compound having the formula Y—R″— YProt, and

 (ii) converting YProt in the reaction product from (i) to Y′, and

 (iii) reacting the product from (ii) with a compound of formula Ia or Ib to yield a compound of formula IIIa or IIIb;

wherein:

Y, Y′ are independently selected from OH, I, Br, Cl, mesylate or tosylate;

YProt is a precursor to Y′ or a chemically protected form of Y′ having a protecting group that is orthogonal to R 10 and R 11 .

12. A method according to claim 11 , wherein Y and Y′ are I.

13. A method according to claim 11 , wherein Y is OH and YProt is O-benzyl.