Design, synthesis, and characterization of novel, nonquaternary reactivators of GF-inhibited human acetylcholinesterase.

The goal of this research was to identify structurally novel, non-quaternarypyridinium reactivators of GF (cyclosarin)-inhibited hAChE that possess the capacity to mediate in vitro reactivation of GF-inhibited human acetylcholinesterase (hAChE). New compounds were designed, synthesized and assessed in GF-inhibited hAChE assays. Structure activity relationships for AChE binding and reactivation of GF-inhibited hAChE were developed. Lead compounds from two different chemical series, represented by compounds 17 and 38, displayed proficient in vitro reactivation of GF-inhibited hAChE, while also possessing low inhibition of native enzyme.

Targeting HER2-positive cancer with dolastatin 15 derivatives conjugated to trastuzumab, novel antibody-drug conjugates.

PURPOSE: Targeting tubulin binders to cancer cells using antibody-drug conjugates (ADCs) has great potential to become an effective cancer treatment with low normal tissue toxicity. The nature of the linker used to tether the tubulin binder to the antibody and the conjugation sites on the antibody and the small molecule are important factors in the ADC stability and effectiveness. METHODS: We explored the use of tubulin-targeting dolastatin 15 derivatives (Dol15) tethered covalently to a representative antibody, trastuzumab, via cleavable and non-cleavable linkers at varying antibody reactive sites (i.e., lysine residues, partially reduced hinge region disulfide bonds) and drug coupling sites (i.e., C-terminus, N-terminus), to investigate which constructs were more effective in killing HER2-positive cells in vitro and in vivo. RESULTS: We found that Dol15 conjugated to trastuzumab via lysine residues at the drug C-terminus using a non-cleavable linker (trastuzumab-amide-C-term-Dol15) produced target-dependent growth inhibition of cells endogenously expressing high HER2 levels (i.e., SK-BR-3, SK-OV-3) in vitro. This ADC was effective at varying doses (i.e., 10 and 20 mg/kg) in the SK-OV-3 human ovarian cancer xenograft. CONCLUSIONS: Tethering Dol15 via partially reduced disulfide bonds at the drug C-terminus via a non-cleavable linker (trastuzumab-MC-C-term-Dol15) resulted in an equally effective ADC in vitro, showing that site of antibody conjugation did not influence ADC activity. However, tethering Dol15 at the drug N-terminus using non-cleavable and cleavable linkers (trastuzumab-MC-N-term-Dol15 and trastuzumab-MC-VC-PABC-N-term-Dol15, respectively) resulted in ineffective ADCs. Thus, Dol15 tethered at the C-terminus may be a useful tubulin-targeting agent for conjugation at various antibody reactive sites.

Synthetic studies on formamidopyrimidines related to clofarabine.

Degradation of clofarabine (3) in 0.9% saline solution at 100 degrees C afforded three degradation products which were determined to be formamidopyrimidines 4-6. Compounds 4 and 5 were assigned as C(1') anomers on the basis of one-dimensional and two-dimensional NMR experiments, whereas 6 was found to be the formamidopyrimidine lacking the sugar moiety. An improved procedure for the synthesis of formamidopyrimidines was developed, wherein benzoylated clofarabine (11) was treated with allyl chloroformate, followed by deprotection of the alloc group with catalytic Pd(PPh(3))(4) and dimedone. A synthesis of compound 6 from 4 is also described.

Discovery and development of clofarabine: a nucleoside analogue for treating cancer.

The treatment of acute leukaemias, which are the most common paediatric cancers, has improved considerably in recent decades, with complete response rates approaching approximately 90% in some cases. However, there remains a major need for treatments for patients who do not achieve or maintain complete remission, for whom the prognosis is very poor. In this article, we describe the challenges involved in the discovery and development of clofarabine, a second-generation nucleoside analogue that received accelerated approval from the US FDA at the end of 2004 for the treatment of paediatric patients 1-21 years old with relapsed or refractory acute lymphoblastic leukaemia after at least two prior regimens. It is the first such drug to be approved for paediatric leukaemia in more than a decade, and the first to receive approval for paediatric use before adult use.

Preparation of a fludarabine intermediate via selective alkylation of 2-fluoroadenine.

The reaction between 2-fluoroadenine (3) and 1,3,5-tri-O-benzyl-1-alpha-D-chloroarabinofuranose (4) with potassium t-amylate was evaluated in various solvents to afford 9-beta-D-(2,3,5-tri-O-benzyl-arabinofuranosyl)-2-fluoroadenine (5) and the corresponding alpha-anomer (6). In addition, 7-beta-D-(2,3,5-tri-O-benzyl-arabinofuranosyl)-2-fluoroadenine (7) and an unusual "bis-fluoroadenine" nucleoside (8) were isolated as byproducts. The highest anomeric ratio (beta/alpha > 10) and conversion (> 80%) were observed with the highly polar solvent sulfolane. This reaction was demonstrated on gram scale as a practical laboratory synthesis of 5, a known intermediate in the synthesis of fludarabine.

Formal synthesis of angiogenesis inhibitor NM-3.

We report the formal synthesis of angiogenesis inhibitor NM-3 (1) in six steps from either of the 2,4-dimethoxyhalobenzenes 13a,b or 3,5-dimethoxychlorobenzene (13c). The first key reaction is the regiospecific alkylation/rearrangement between the aryne derived from 13a-c with sodium diethylmalonate in THF to produce diester 11, which after hydrolysis and cyclization affords homophthalic anhydride 3. The second is the reaction of anhydride 3 with either ethyl 2-methylmalonate (28a), in the presence of 1,1'-carbonyldiimidazole, or ethyl-2-methylmalonyl chloride (28b) under basic conditions to afford key isocoumarin 27. The conversion of 27 constitutes a formal synthesis of NM-3.