Pivaloyloxymethyl Research Articles

Synthesis and hybridization properties of oligonucleotides having 4-N-(pyrrol-2-ylcarbonyl)deoxycytidine

A new 4-N-acylated deoxycytidine derivative, 4-N-(1H-pyrrol-2-ylcarbonyl)deoxycytidine, was synthesized and found to be stable under rather basic conditions. Oligodeoxynucleotides (ODNs) incorporating this modified deoxynucleoside at various positions were successfully synthesized by using a pivaloyloxymethyl (POM) group for protection of the pyrrole residue. The POM group was removed by treatment with 1.5 M NaOMe/MeOH. ODNs containing modified deoxycytidines exhibited hybridization properties superior to those of the unmodified ODNs. We found the acylation of the cytosine base with an aromatic acyl-type substituent led to significant increase of the thermo stability of DNA duplexes. This is the first noteworthy observation in this kind of modification. The synthesis and hybridization properties of 4-N-(1H-pyrrol-2-ylcarbonyl)deoxycytidine derivatives will be also reported.

Synthesis of aza-analogues of Ganciclovir

Aza-analogues of ganciclovir have been prepared via coupling of nucleobases with N-[2-pivaloyloxy-1-(pivaloyloxymethyl)ethyl]methanesulfonamide or 3-mesyl-4-(benzoyloxymethyl)-1,3-oxazolidine.

Chemical Development of ZD9331: Synthesis of a Bromomethylquinazolinone Avoiding a Nonselective Radical Bromination

An efficient regiospecific synthesis of ZD9331 Pivaloyloxymethyl (POM) Bromide (4) has been accomplished via ZD9331 Quinacetate HCl (15) avoiding a nonselective bromination. The original route used a radical bromination on a substrate with three methyl groups, which generated a range of bromomethyl derived compounds that carried through to the final active pharmaceutical ingredient (API). A strategy, based on the Zinin reaction, was developed to synthesize the required bromomethyl compound in a regioselective manner. This approach was successfully scaled to manufacture a tonne of material.

Prodrug forms of N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate, a potent inhibitor of folylpoly-gamma-glutamate synthetase: synthesis and hydrolytic stability.

Ester prodrugs of the phosphinate pseudopeptide N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate (1a) were synthesized. H-phosphinic acids derived from N-Cbz vinyl glycine esters were converted to the desired pseudopeptides by Michael addition to alpha-methyleneglutarate esters. Pivaloyloxymethyl (POM) ester moieties were incorporated in both the N-terminal and C-terminal fragments prior to formation of either C-P bond. N-Alkylation of the corresponding amides derived from p-(N-methyl)aminobenzoic acid with 2,4-diamino-6-(bromomethyl)pteridine gave the target compounds. POM esters of methotrexate and the corresponding gamma-glutamyl conjugate were also synthesized using the same strategy. All prodrugs were evaluated in Chinese hamster ovary cells. Although the pseudopeptide prodrugs were ineffective, prodrugs of methotrexate and the corresponding gamma-glutamyl conjugate were equipotent with the parent compounds. Stability of the prodrugs was investigated in both phosphate buffer and cell line medium to provide a rationale for the observed biological data.

Trouble with Potassium Carbonate and Centrifuges: Mass Transfer and Scale-Up Effects in the Manufacture of ZD9331 POM Quinacetate

Manufacture of ZD9331 pivaloyloxymethyl (POM) quinacetate, was progressively scaled up from large-scale lab to pilot plant to full-scale production. The specific surface area of the potassium carbonate used for the deprotonation was found to be critical as successive increases in the mass transfer area were counteracted by the reduced mass transfer efficiency, linked to the reactor size and impeller effectiveness. Furthermore, a change from a pressure filter to a centrifuge meant that the washing efficiency was similarly limited by mass transfer, with the rate of dissolution of the undesired regioisomer on the centrifuge being too low for the shorter wash time. These problems were overcome, resulting in two successful manufacturing campaigns with over 1 tonne of POM quinacetate produced well within specification in eight batches.

Synthesis of novel C4-linked imidazole ribonucleoside phosphoramidites for probing general acid and base catalysis in ribozyme

We describe the synthesis of novel C4-linked imidazole ribonucleoside phosphoramidite (PA) 1a by which the imidazole moiety is incorporated into VS ribozyme to study its role in general acid and base catalysis. Investigation of protecting groups for the imidazole- N first indicated that pivaloyloxymethyl (POM) was adequate as an N-protecting group for the imidazole nucleoside, which could be readily removed under mild basic conditions. Further, the synthetic method was extended to synthesis of 2′-deoxy- and 2′- O-allyl nucleoside PAs 1b and 1c .

Current Prodrug Strategies for the Delivery of Nucleotides into Cells

Nucleosides are currently used in the treatment of many infections caused by viruses and against various cancers. The principal historic limitations of the development of nucleoside drugs that either directly inhibit DNA or RNA polymerases or that inhibit RNA and DNA replication by virtue of their ability to act as alternative substrates for these polymerases, have been the requirements for cellular penetration of the uncharged nucleosides and their subsequent biological conversion to the pharmacologically active nucleoside triphosphate (NTP) species. Unfortunately, intracellular phosphorylation of nucleosides frequently results in toxic by-products, limiting the drug dose that can be administered. In the past few decades, intensive research has provided insights into the nature of chemical and biological requirements associated with the in vitro selective delivery of nucleotides into cells. As such, cleavable protecting groups represent a very powerful tool to increase not only drug delivery but also bioavailability. This review presents an update of prodrug strategies in which the most prominent masking groups currently in use for the treatment of cancer and viral diseases, their stability, toxicities and biological activities are discussed. In particular, the following prodrugs: S-acyl-2-thioethyl (SATE), pivaloyloxymethyl (POM), isopropyloxycarbonyloxymethyl (POC), amino acid esters, and polyethylene glycol drug conjugates will be addressed.

Synthesis of acyloxymethyl ester prodrugs of the transferable protein farnesyl transferase substrate farnesyl methylenediphosphonate

Three isoprenoid diphosphate analogues of farnesyl diphosphate (FPP) where the diphosphate has been replaced by methylene diphosphonate and the negative charges masked by frangible pivaloyloxymethyl (POM) esters were prepared. Farnesyl methylenediphosphonate is a sub-micromolar substrate for protein farnesyl transferase. The tripivaloyloxymethyl esters of isoprenoid methylenediphosphonate have significantly increased lipophilicity and may act as important farnesyl diphosphate prodrugs.

A Synthetic Route to Cell Permeable, Macrocyclic-Based Phosphonate Acyloxymethyl Esters

Four cell membrane-permeant derivatives of polyaza macrocyclic ligands, including acetoxymethyl (AM) and pivaloyloxymethyl (POM) esters of 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetrakis(ethyl methylenephosphonate) (DOTPME) and 1,4,7-triazacyclononane- 1,4,7-tris(ethyl methylenephosphonate) (NOTPME), were prepared as model systems for the detection of intracellular ions by 31P NMR spectroscopy. Preliminary results on isolated perfused rat hearts suggest that such ligands may be useful for monitoring intracellular levels of Ca2+ and Mg2+.

Synthesis of C4-linked imidazole ribonucleoside phosphoramidite with pivaloyloxymethyl (POM) group

A novel C4-linked imidazole ribonucleoside phosphoramidite was designed and successfully synthesized starting from tribenzylribofuranosylimidazole. This phosphoramidite product enables incorporation of the imidazole moiety into an RNA sequence and hence allows study of its role in the general acid and base catalysis of ribozymes. Pivaloyloxymethyl (POM) was first introduced as an N-protecting group for the imidazole ribonucleoside that can be readily removed under mild basic condition.

AS-924, a novel, orally active, bifunctional prodrug of ceftizoxime: physicochemical properties, oral absorption in animals, and antibacterial activity

AS-924 is an oral prodrug of the antibiotic ceftizoxime (CTIZ), a parenteral use cephalosporin. This novel prodrug, produced by esterifying CTIZ with a lipophilic pivaloyloxymethyl (POM) group and introducing a water soluble l-alanyl group, is expected to increase the bioavailability and thereby, augment the antibacterial activity of CTIZ in vivo compared with existing prodrugs. To study the effect of the l-alanyl group in AS-924 on its bioavailability, the plasma concentration profiles of CTIZ in dogs were examined following the dosing of AS-924 and CTIZ-POM, in powder form, after pretreatment with the antacid ranitidine, and following the dosing of AS-924 after pretreatment with a gastrointestinal motility stimulant metoclopramide or suppressant scopolamine butylbromide. The absorption rate of AS-924 was constant under these different conditions due to its unique balance of lipophilicity and water solubility. CTIZ is as antibacterially active as pre-existing oral cephalosporins against Gram-positive clinical isolates, while being more active against all Gram-negative isolates-particularly Enterobacteriaceae and Haemophilus influenzae. A simulation model for the eradication profile of bacteria in computer programmed pharmacokinetic (PK) system was carried out to study the antibacterial action of CTIZ in human. CTIZ was proven to eradicate Streptococcus pneumoniae and H. influenzae effectively, while cefpodoxime (CPOD), the active moiety of CPOD proxetil, eradicated S. pneumoniae, but not H. influenzae. These results confirm that, AS-924 is a potent oral antibiotic and would be expected to be clinically effective and efficient.

A short-step synthesis of orally active carbapenem antibiotic CS-834.

An orally bioavailable carbapenem CS-834, which is a pivaloyloxymethyl (POM) ester-type prodrug and has (R)-5-oxopyrrolidin-3-ylthio moiety at the C-2 position of the 1 beta-methylcarbapenem skeleton, is currently under clinical trial. We accomplished a short-step synthesis of CS-834 by using phosphorus ylide from the intramolecular Wittig-type reaction in the key step for cyclization to the bicyclic carbapenem system. The POM ester group was found to be suitable for the cyclization conditions.

Sensitive semi-microcolumn high-performance liquid chromatographic method for the determination of DU-6681, the active parent drug of a new oral carbapenem antibiotic, DZ-2640, in human plasma and urine using a column-switching system as sample clean-up procedure

DZ-2640 is a new oral carbapenem antibiotic having a dihydro-pyrroloimidazole ring as a side chain and a pivaloyloxymethyl (POM) ester prodrug of DU-6681, the active parent compound. A simple and sensitive column-switching semi-microcolumn high-performance liquid chromatographic method for the determination of DU-6681 in human plasma and urine has been developed. Human plasma was diluted with an equal volume of 1 M MOPS buffer (pH 7.0) and the mixture was filtered through an Ultrafree C3GV. The resulting filtrate was injected without further cleanup onto the HPLC system. Human urine was diluted with an equal volume of 1 M MOPS buffer (pH 7.0) and the mixture was directly injected onto the HPLC system. The analyte was detected by monitoring the column effluent with UV light at a wavelength of 300 nm, which resulted in the limit of quantitation of 0.008 μg/ml of plasma and 0.32 μg/ml of urine. Calibration curves were linear in the range of 0.008 to 5.85 μg/ml in plasma and 0.32 to 104.4 μg/ml in urine. The present methods showed greatly increased sensitivity for DU-6681 compared to conventional HPLC methods and also showed satisfactory recovery, selectivity, precision, and accuracy. Stability studies showed that 1 M MOPS buffer (pH 7.0) acted as a stabilizer. In plasma and urine diluted with equal volume of the buffer, DU-6681 showed good stability at −80°C for up to 4 weeks with no significant loss of the drug.

14C-NaVP and 14C-PEV repeated dose study in rat. Pharmacokinetic study in rats after repeated oral administrations of 14C-valproic acid sodium salt and 14C-valproic acid pivaloyl oxymethyl ester.

The absorption, excretion and tissue distribution of radioactivity after repeated oral equimolar doses of 14C-valproic acid sodium salt (NaVP) or 14C-valproic acid pivaloyl oxymethyl ester (PEV) was investigated in male rats treated once a day for 14 consecutive days. The 14th day plasma time-course of radioactivity after PEV administrations was characterised by a slow absorption rate with a delayed peak (tmax 2 h, Cmax 7.52 +/- 1.35 microg eq./ml), followed by a plateau lasting up to 8 h. After NaVP treatment, the main peak of radioactivity was observed 0.5 h after administration (Cmax 8.30 +/- 1.26 microg eq./ml) followed by a secondary peak due to biliary enterohepatic recycling. Starting from 4 h onwards, radioactivity levels after PEV treatment were higher than those after NaVP (AUCtau = 113.3 h.microg eq./ml after PEV vs 71.9 h.microg eq./ml after NaVP), but concentrations declined with similar terminal half-lives (52.8 h for PEV and 49.7 h for NaVP). Radioactivity recovered (0-432 h interval) in urine accounted for 79.3% (PEV) and 56.1% (NaVP) while, in faeces accounted for 9.1% (PEV) and 26.1% (NaVP) of total administered dose (14 days). The difference is attributable to a higher excretion of radioactivity in the bile for NaVP. The missing fraction in the total radioactivity balance is probably excreted in expired air, as observed in single dose studies. Radioactivity excreted in bile (0-8 h interval of the last 14th day) accounted for 5.1% (NaVP) and 0.23% (PEV) of the total administered dose (14 days). A possible explanation of this difference may be a different metabolism pattern for the two compounds. The negligible biliary excretion observed after PEV administration is probably due to an inhibition of the glucuronation of valproic acid (or other metabolites) caused by the pivalic acid. Due to the presence of the enterohepatic recycle, the radioactivity levels in intestine, 0.5 and 2 h after administration, were higher after NaVP administration. According to higher plasma levels, the radioactivity concentrations in liver, kidneys and some fat tissues were found to be slightly higher after PEV administration. At 120 h after the last treatment of both compounds, relevant tissue concentrations were observed in mesenteric lymphnodes, perirenal and brown fat. The tissue-plasma radio activity ratio appeared quite similar for the two compounds.

Comparison of Cytotoxicity of Mononucleoside Phosphotriester Derivatives Bearing Biolabile Phosphate Protecting Groups in Normal Human Bone Marrow Progenitor Cells

The effects of three mononucleoside phosphotriester derivatives of 3′-azido-2′,3′-dideoxythymidine (AZT) which incorporate biolabile phosphate protecting groups, namely S-acetyl-2-thioethyl (MeSATE), S-(2-hydroxyethylsulfidyl)-2-thioethyl (DTE), and pivaloyloxymethyl (POM) were studied and compared to their nucleoside parent in human myeloid colony-forming cells. Moreover, the relative antiviral potency of these three pronucleotides were determined in primary human peripheral blood mononuclear cells infected with human immunodeficiency virus type 1. The results indicate that the SATE and DTE pro-moieties, as well as their degradation products, do not induce additional toxicity. The bis(MeSATE) phosphotriester derivative of AZT emerged as the most selective inhibitor with an in-vitro therapeutic index of the same order of magnitude as observed for AZT. This study has been extended to the corresponding bis(MeSATE) and bis(DTE) phosphotriester derivatives of 2′,3′-dideoxyuridine (ddU).

Synthesis, in vitro antiviral evaluation, and stability studies of bis(S-acyl-2-thioethyl) ester derivatives of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) as potential PMEA prodrugs with improved oral bioavailability.

A new series of hitherto unknown 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA) phosphonodiester derivatives incorporating carboxyesterase-labile S-acyl-2-thioethyl (SATE) moieties as transient phosphonate-protecting groups was prepared in an attempt to increase the oral bioavailability of the antiviral agent PMEA. We report here a direct comparison of the in vitro anti-HIV and anti-HSV activities as well as the in vitro stability between the bis(SATE) derivatives and the already known PMEA prodrugs, namely, bis[(pivaloyloxy)methyl (POM)]- and bis[dithiodiethyl (DTE)]PMEA. All of the compounds tested showed an enhanced in vitro antiviral activity compared to the parent PMEA. The bis(POM)- and bis(tBu-SATE)PMEA derivatives were the most effective. However, striking differences between these two compounds were found during the stability studies. In particular the bis(tBu-SATE)PMEA was found to be more stable than bis(POM)PMEA in human gastric juice and human serum, suggesting it could be considered as a promising candidate for further in vivo development.

Synthesis of 6,6‐disubstituted penems

AbstractThe synthesis of a series of 6,6‐disubstituted penems starting from penicillanate 5a is described. These penems were isolated and characterized as their pivaloyloxy methyl ester.

Orally active pivaloyloxymethyl 3-(isoxazolidin-5-yl)cephalosporins.

Orally active pivaloyloxymethyl 3-(isoxazolidin-5-yl)cephalosporins.

A cyclic AMP phosphodiesterase inhibitor, 8'-pivaloyloxymethyl ester (POM-ester) of griseolic acid, lowers rabbit intraocular pressure.

The effects of griseolic acid (GA), a cyclic-AMP phosphodiesterase (PDE) inhibitor, and its 8'-pivaloyloxymethyl (POM) ester on intraocular pressure (IOP) in rabbits were investigated. When 50 microliters of 1 and 2% GA POM ester solutions were topically applied to one eye in normal rabbits, significant IOP decreases were detected at 2 hrs and at 1 to 5 hrs, respectively. Other than ocular hypotension, no other ocular effects were detected locally even after administration of 2% GA POM ester. A more marked reduction in IOP occurred after the intravitreal injection of the GA POM ester. IOP was also reduced when GA was used in an intravitreal injection but not when it was topically applied. The difference in permeability between GA and GA POM ester across the corneal epithelium may explain why GA failed to reduced IOP following topical administration. GA and the GA POM ester inhibited cAMP PDE in rabbit ciliary body at low concentrations, the I50 being 0.075 microM and 2.4 microM, respectively, with 0.25 microM cAMP as substrate. GA and the GA POM ester markedly increased cAMP levels in vitro in iris-ciliary body specimens. Possibly, GA POM ester or its analogues may represent a new mechanistic class of ocular hypotensive agents.

Bridged Oxacephems; Part 2. Synthesis of 7α-[(R)-1-Hydroxyethyl]-2β,7β-methano-1-oxacephems1

Highly strained 2β,7β-methano-1-oxacephem esters with the thienamycin-type [(R)-1-hydroxyethyl] side chain at 7α, 16a and 16b, were successfully synthesized in a highly stereoselective manner. X-ray crystallography of 16a showed very high distortion of the oxacephem moiety in 16, as suggested by the high frequency IR absorption at 1791 cm-1, and showed an h value of 0.52 Å which slightly exceeded the h values of 0.49-0.50 Å for the carbapenem nucleus. Having this highly strained structure, the compounds were very fragile, and in particular, the pivaloyloxymethyl (POM) ester 16b decomposed within a few hours even when left standing in a refrigerator. As expected from its instability, this compound showed no antibacterial activity in an assay performed in the presence of horse serum.