Synthesis and biological evaluation of purine-containing butenolides

6 -Chloropurine derivatives of gamma-(Z)-ethylidene- 2,3 -dimethoxybutenoli de 3a, gamma-(Z)-ethylidene2-methoxy- 3-(4-nitro)benzyloxybutenolide 3b, ga mma-(Z)-ethylidene-2 -(4-nitro)benzyloxy-3-methoxybutenolide 3c, gamma-(Z)- ethylidene-2,3-di(4-nitro)benzyloxybutenolide 3d, and dimethylphosphonoy-(Z )-ethylidene-2,3-dimethoxybutenolide 11 as well as the adenine derivative o f gamma-(Z)ethylidene-2,3-dimethoxybutenolide 6 were synthesized. The key s teps in the high-yield synthesis of 6 involved hydration/dehydration of the C-4=C-5 in the precursor 3a. In the presence of NH4OH at elevated temperat ure, 3a underwent a reverse Michael-type addition with water to produce hyd rate 5. At 37 degreesC, 6 was also hydrated in the presence of S-adenosyl-L -homocysteine hydrolase to afford 5. Butenolide 6 exhibited an inhibitory p roperty toward the enzyme. Such type II (enzyme-mediated addition of water across C-4=C-5) mechanism is the first example of "enzyme-substrate interme diate" inactivation of S-adenosyl-L-homocysteine hydrolase. In contrast wit h type I mechanism-based inactivation, reduction of enzyme-bound NADP+ to N ADPH was not observed. Upon treatment with HCl, stereoselective dehydration of 5 occurred to give the target molecule 6. At ambident temperature, 3a w as hydrated in the presence of NH4OH or pig liver esterase to produce 6-chl oropurine derivative 4. An unambiguous proof of the structures of 3-5 was o btained by X-ray crystallographic analysis. For the synthesis of phosphonat e derivative 11, the key step involved chlorination of phosphonate 9 by use of CF3SO2Cl and 1,8-diazabicyclo [5.4.0]undec-7-ene in CH2Cl2. 6-Chloropur ine-containing butenolide 3d, 6-chloropurine derivative of 4-hydroxybutenol ide 4, and adenine-containing 4-hydroxybutenolide 5 did not show anticancer and antiviral activities. 6-Chloropurine-containing ethylidene-2,3-dialkox ybutenolides 3a-c and phosphonate 11, however, exhibited inhibitory activit y against murine leukemias (L1210 and P388), breast carcinoma (MCF7), and h uman T-lymphoblasts (Molt4/C8 and CEM/O) cell lines. They were also notably active toward thymidine kinase-deficient varicella-zoster virus (TK-VZV). Adenine-containing ethylidene2,3-dimethoxybutenolide 6 exhibited marked sel ectivity in cytostatic activity against the murine leukemia (P388) cell lin e.