Analogs of leucascandrolide A

1. A compound of the formula (I) or a salt, enantiomer or racemate thereof:

wherein:

R 1 is —(C 0-15 alkylene)-L-(C 0-15 alkylene)-Z 4

wherein each alkylene group in R 1 independently contains from 0 to 3 double or triple bonds; and wherein each alkylene group of R 1 may be unsubstituted or substituted;

L is a bond, substituted or unsubstituted heterocyclyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, —(CH 2 CH 2 O) a —, —CONR i —, —NR i CO—, —C(O)—, —S—, —S(O)— or —S(O) 2 —;

Z 4 is hydrogen, —NR i R vi , —OR vi , —SR vi , or —CONR i R vi ;

R 2 is C 1-3 alkyl;

R 3 is hydrogen, C 1-6 alkyl, —OR i , —SR i , or —O(CO)R i ;

R 4 is hydrogen or C 1-6 alkyl;

each X and X′ are independently O or NR i ;

each Y and Y′ are independently O or S;

each of Z 1 , Z 2 , and Z 3 , is independently selected from CR i , N, O or S;

the alkylene groups within the substituent on C5 may independently contain from 1 to 2 double bonds;

a is an integer from 1-10;

each R i is independently hydrogen or C 1-6 alkyl; and

R vi is hydrogen, C 1-6 alkyl, or a label;

provided that if X, X′, Y, and Y′ are O, R 2 is methyl, R 3 is methyl, and R 4 is methyl or hydrogen, then R 1 is not —CH═CHCH 2 CH(CH 3 ) 2 , CH 2 CH 2 CH 2 CH(CH 3 ) 2 , C≡CCH 2 CH(CH 3 ) 2 , —CH 3 or —H.

2. The compound of claim 1 , wherein at least one alkylene group of R 1 is substituted with from 1 to 3 substituents selected from alkyl, halogen, —NR i R ii , —OR i , —SR i , —CN, —NO 2 , ═O, —OC(O)R i , —C(O)R i , —C(O)NR i R ii , —OC(O)NR i R ii , —NR ii C(O)R i , —NR i C(O)NR iii R ii , —CO 2 R i , —NR i R ii , —NR ii CO 2 R i , —SR i , —S(O)R i , —S(O) 2 R i , —S(O) 2 NR i R ii , —NR i S(O) 2 R ii , unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl, and unsubstituted or substituted heterocyclyl, wherein each R i , R ii and R iii are independently hydrogen or C 1-6 alkyl.

3. The compound of claim 1 , which is of the formula (II):

4. The compound of claim 1 , wherein Z 1 is N, Z 2 is CH, and Z 3 is O.

5. The compound of claim 1 , wherein X is O.

6. The compound of claim 1 , wherein Y is O.

7. The compound of claim 1 , wherein L is a bond, substituted or unsubstituted 5- or 6-membered heterocyclyl, substituted or unsubstituted phenyl, or substituted or unsubstituted 5- or 6-membered heteroaryl.

8. The compound of claim 1 , wherein Z 4 is —NR i R vi .

9. The compound of claim 1 , where R vi is an affinity label or fluorescent marker.

10. The compound of claim 1 , where R 3 is OR i .

11. The compound of claim 1 , where R 4 is hydrogen or methyl.

12. The compound of claim 1 , wherein R 1 is —C 1-15 alkynyl.

13. The compound of claim 1 , wherein R 1 is —(C 1-8 alkylene)-L-(C 1-6 alkylene)-Z 4 .

14. The compound of claim 1 , wherein R 1 is —(C 1-8 alkylene)-L-(C 1-6 alkylene)-NR i R ii , where L is a unsubstituted or substituted 5- or 6-membered heterocyclyl, unsubstituted or substituted 5- or 6-membered heteroaryl, or unsubstituted or substituted phenyl.

15. The compound of claim 1 , which is selected from the group consisting of:

16. A compound of the formula (III) or a salt, enantiomer or racemate thereof:

wherein

R 1 is —(C 0-15 alkylene)-L-(C 0-15 alkylene)-Z 4

wherein each alkylene group in R 1 independently contains from 0 to 3 double or triple bonds; and wherein each alkylene group of R 1 may be unsubstituted or substituted;

L is a bond, substituted or unsubstituted heterocyclyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, —CONR i —, —NR i CO—, —C(O)—, —S—, —S(O)— or —S(O) 2 —;

Z 4 is hydrogen, —NR i R ii , —OR i , —SR i , or —CONR i R ii ;

R 3 is hydrogen, C 1-6 alkyl, —OR i , —SR i , or —O(CO)R i ;

R 4 is hydrogen or C 1-6 alkyl;

X is OR iii ;

X′ is O or NR i ;

Y′ is O or S;

each R i and R ii are independently hydrogen or C 1-6 alkyl; and

R iii is a hydroxy-protecting group,

provided that if X, X′, Y, and Y′ are O, R 2 is methyl, R 3 is methyl, and R 4 is methyl or hydrogen, then R 1 is not —CH═CHCH 2 CH(CH 3 ) 2 , CH 2 CH 2 CH 2 CH(CH 3 ) 2 , C≡CCH 2 CH(CH 3 ) 2 , —CH 3 or —H.

17. The compound of claim 16 , which is selected from the group consisting of:

or a salt, enantiomer or racemate thereof.

18. A composition comprising a pharmaceutically acceptable carrier and the compound of the formula (I):

wherein:

R 1 is —(C 0-15 alkylene)-L-(C 0-15 alkylene)-Z 4

wherein each alkylene group in R 1 independently contains from 0 to 3 double or triple bonds; and wherein each alkylene group of R 1 may be unsubstituted or substituted;

L is a bond, substituted or unsubstituted heterocyclyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, —(CH 2 CH 2 O) a —, —CONR i —, —NR i CO—, —C(O)—, —S—, —S(O)— or —S(O) 2 —;

Z 4 is hydrogen, —NR i R vi , —OR vi , —SR vi , or —CONR i R vi ;

R 2 is C 1-3 alkyl;

R 3 is hydrogen, C 1-6 alkyl, —OR i , —SR i , or —O(CO)R i ;

R 4 is hydrogen or C 1-6 alkyl;

each X and X′ are independently O or NR i ;

each Y and Y′ are independently O or S;

each of Z 1 , Z 2 , and Z 3 , is independently selected from CR i , N, O or S;

the alkylene groups within the substituent on C5 may independently contain from 1 to 2 double bonds;

a is an integer from 1-10;

each R i and R ii are independently hydrogen or C 1-6 alkyl; and

R vi is hydrogen, C 1-6 alkyl, or a label.