Studies Of Pentostatin Synthesis And Quality Control

Pentostatin is a kind of purine analog which was originally isolated from the species of bacteria Streptomyces antibioticus. Pentostatin has shown dramatic antitumor effects to hairycell leukemia, lymphoma and chromic lymphocytic leutemia. In 1998, FDA approved pentostatin as the anti-tumor drug used to treat acute leukaemia. There are a few literatures about the pentostatin synthesis, but most of them focus on the laboratory trial with lower yield. And there is no record about Pentostatin synthesis and no API production record in SFDA in China. Pentostatin synthesis and quality control research work is discussed on the following three parts.The first part is study on Pentostatin synthesis route and process parameters.1. Three synthesis routes of 6,7-Dihydro-3H-imidazo[4,5-d][l,3]diazepin-8-one were compared.Much effort was placed on one of the synthesis route,which was accomplished in 8 steps started from 5-nitroimidazole.The process of nitromethane, nitrate deduction and coupling steps are optimized. The instability issue of 6,7-Dihydro-3H-imidazo[4,5-d][1,3]diazepin-8-one was resolved by optimized process procedure.2. The synthesis of the aglycon fragment,2-deoxy-3,5-di-O-p-Toluoyl-pento-furanosyl, was achieved in 3 steps from 2-deoxy-D-ribose,which underwent methylation, toluyl protection and chloronation. The 6,7-Dihydro-3H-imidazo [4,5-d][1,3]diazepin-8-one heterocyclic moiety is glycosylated by aglycon with Tin(IV) chloride to get the mixture ofβand a ketone. The mixture ofβand a ketone was purified by crystallization and column purification to get the pureβ-ketone. Tin(IV) chloride as Lewwis acid catalyst improved the glycoslation yield more than 20% than that reported on the literature.3. The final product Pentostatin was synthesized fromβ-ketone by two synthesis routes. One isβ-ketone hydrogenated by NaBH4 to get 1:1 R/S chiral alcohol, then purified by pre-HPLC to get the Pentostatin. Another route is asymmetric transfer hydrogenation. A new catalyst, di-μ-chloro-bis [(p-cymene)chlororuthenium(II) coordinated with (1R,2R)-N-(p-Toluenefulfonyl)-1,2-diphenylethanediamene, was used forβ-ketone hydrogenation with 99:1 R/S chiral alcohol. One of the challenges, a chiral alcoholic center in the C-8 is successfully achieved by this catalyst. The yield of 2nd route increased 70% than the 1st route and the process is simplified dramatically.The second part is Pentostatin quality control study.Pentostain has not been recorded by any pharmacopeial yet. So it is necessary to set up the final product specification to control the quality. Also the intermediate and final product test methods were developed. Meanwhile the HPLC and HS-GC method validation were performed. Furthermore, The main known impurities, Pentostatin isomers were identified.The third part is Pentostatin pilot scale production.Based on the trial data, the economic and practical synthesis route is used to pilot production. During the pilot, some process parameters were adjusted. Pentostatin was produced in a total 12 steps with 1.3% yield.