Patent ID: 7569594

Claim:
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.