5-Amino-4-(diazoacetyl)-1-beta-D-ribofuranosylimidazole, a new antileukemic agent

Design, synthesis, and characterization of a series of cytochrome P(450) 3A-activated prodrugs (HepDirect prodrugs) useful for targeting phosph(on)ate-based drugs to the liver

A new class of phosphate and phosphonate prodrugs, called HepDirect prodrugs, is described that combines properties of rapid liver cleavage with high plasma and tissue stability to achieve increased drug levels in the liver. The prodrugs are substituted cyclic 1,3-propanyl esters designed to undergo an oxidative cleavage reaction catalyzed by a cytochrome P(450) (CYP) expressed predominantly in the liver. Reported herein is the discovery of a prodrug series containing an aryl substituent at C4 and its use for the delivery of nucleoside-based drugs to the liver. Prodrugs of 5'-monophosphates of vidarabine, lamivudine (3TC), and cytarabine as well as the phosphonic acid adefovir were shown to cleave following exposure to liver homogenates and exhibit good stability in blood and other tissues. Prodrug cleavage required the presence of the aryl group in the cis-configuration, but was relatively independent of the nucleoside and absolute stereochemistry at C4. Mechanistic studies suggested that prodrug cleavage proceeded via an initial CYP3A-catalyzed oxidation to an intermediate ring-opened monoacid, which subsequently was converted to the phosph(on)ate and an aryl vinyl ketone by a beta-elimination reaction. Studies in primary rat hepatocytes and normal rats comparing 3TC and the corresponding HepDirect prodrug demonstrated the ability of these prodrugs to effectively bypass the rate-limiting nucleoside kinase step and produce higher levels of the biologically active nucleoside triphosphate.

Design, synthesis and structure-activity relationships of a series of 9-substituted adenine derivatives as selective phosphodiesterase type-4 inhibitors

Adenine derivatives substituted in position 9 have been demonstrated to have potent cyclic nucleotide phosphodiesterase (PDE) inhibition properties with high selectivity toward PDE-4. Starting from our initial lead compound 9-(2-fluorobenzyl)-N(6)-methyl-2-trifluoromethyladenine (4, NCS613), we designed and synthesized a new series of 9-substituted derivatives for developing structure-activity relationship studies. This new series of derivatives showed increased potencies and better selectivity profiles. Structural modifications were achieved in parallel on three different positions of the adenine ring, and led to the following observations: (i) introduction of a lipophilic substituent such as trifluoromethyl, n-propyl group or iodine in the C-2 position is favourable for both the PDE-4 inhibitory activity and the selectivity towards other isoenzymes; (ii) functionalization of the N9 benzyl group with a 2-methoxy substituent led to remarkably more active compounds; (iii) replacement of the N(6)-methylamino moiety by other amino groups is detrimental to the activity. Among all derivatives prepared, the 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), 9-(2-methoxybenzyl)-N(6)-methyl-2-n-propyladenine (9s), and the 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) were found to be the most potent inhibitors within this series (PDE-4-IC(50)=1.4, 7.0, and 0.096 nM, respectively). Compared to our reference compound 4, which showed an IC(50) of 42 nM, the derivative 13b was found 450-fold more potent. Moreover, 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) and 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), were at least 50000-150000 times more selective for the PDE-4 than for the other PDE families. Additionally, these new derivatives showed improved efficiency in inhibiting the TNFalpha release from mononuclear cells from healthy subjects (e.g. adenines 7l, 9s and 13b). Thus, compounds 7l, 9r, 9s and 13b are among the most potent and selective PDE-4 inhibitors reported so far and represent very promising pharmacological tools for a better understanding of the signal transduction involving cyclic AMP within the cell: this pathway is implicated in the physiology and the pathophysiology of inflammation, asthma and autoimmune disorders.

Nonenzymatic synthesis of 5-aminoimidazole ribonucleoside and recognition of its facile rearrangement

5-Amino-1-beta-D-ribofuranosylimidazole 5'-monophosphate (AIR, 1) is the ubiquitous precursor to the purine ribonucleotides in vivo, and it serves as the biochemical precursor to the pyrimidine portion of thiamin (vitamin B1) in certain prokaryotic organisms. The corresponding ribonucleoside (AIRs, 5b) was prepared via chemical (nonenzymatic) synthesis from 5-amino-1-beta-D-ribofuranosylimidazole-4-carboxamide. The tri-O-acetylated derivative of AIRs (5a) was also prepared, and it was shown to undergo a facile ring transformation in aqueous pH 7 buffer to afford N-(imidazol-4-yl)-2,3,5-tri-O-acetyl-D-ribofuranosylamine as a 1:2 mixture of alpha and beta anomers (6a). Under similar conditions, compound 5b affords the corresponding unprotected beta-ribonucleosides 6b. This Dimroth-type ring transformation reaction of 5 to 6, which occurs primarily in neutral aqueous solution, may be responsible for the previously reported lability of AIRs and its derivatives. It may also have relevance to the postulated early biotic pathway to the 9- and 3-substituted purine nucleotide components of an all-purine biopolymer.