Anti-tumor and anti-psoriatic agents

Claim 1

A compound of the formula or a pharmaceutically acceptable salt thereof, wherein X is O or S; Y is O, NH, (H,H), (H,OH) or S; with the proviso that when X is S, Y is not NH, (H,H) or (H,OH); R 1 , R 2 , R 3 and R 4 may be the same or different and each independently is H, C 1 -C 7 alkyl, C 1 -C 7 substituted alkyl, -CHO, CN, -CON(R 8 ,R 9 ), -COOR 7 , -CH=NOR 8 , -CH=NNHCONH 2 , F, Cl, Br, OH, N 3 , -OC 1 -C 7 alkyl, -OC 1 -C 7 substituted alkyl, -OCOR 9 , SH, S(C 1 -C 7 )alkyl, S(C 1 -C 7 )substituted alkyl, SCOR₁₀, S(O) n R₁₁, NH 2 , N(R₁₂,R₁₃), and N( acyl, R₁₄); R 1 , and R 2 taken together may be O, NOH, NOR 8 , =CH 2 or NNHCONH 2 ; R 3 , and R 4 taken together may be O, NOH, NOR 8 , =CH 2 or NNHCONH 2 ; R 1 and R 4 taken together may be a carbon-carbon bond with the proviso that R 2 and R 3 may be the same or different and each independently is selected from the group consisting of H, C 1 -C 7 alkyl, C 1 -C 7 substituted alkyl, -CHO, CN, -COOR 7 , -CON(R 8 , R 9 ), -CH=NOR₁₀, and -CHN=NNHCONH 2 ; R 5 and R 6 are independently H, C 1 -C 7 alkyl, C 1 -C 7 substituted alkyl, F, Cl, Br, OH, N 3 , - OC 1 -C 7 alkyl, - OC 1 -C 7 substituted alkyl, -OCOR₁₅, SH, S(C 1 -C 7 )alkyl, S(C 1 -C 7 ) substituted alkyl, SCOR₁₆, S(O) n R₁₇, NH 2 , N(R₁₈,R₁₉), and N (acyl, R₂₀); R 7 , R 8 , R 9 , R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, and R₂₀ may be the same or different and each independently is H alkyl or substituted alkyl; and n is 1 or 2; with the proviso that R 1 and R 2 may not both be directly attached to the 10-position via a heteroatom and R 3 and R 4 may not both be directly attached to the 11-position via a heteroatom ; and with the still further proviso that the total number of carbon atoms for those R 1 , R 2 , R 3 , and R 4 which are C 1 -C 7 alkyl may not exceed 14; and with the still further proviso that when X and Y are both O, then R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 cannot all be H.