Efficient Synthesis of Carbovir and Its Congener via π-Allylpalladium Complex Formation by Ring Strain-Assisted C−N Bond Cleavage

Palladium-catalyzed benzylation of arylboronic acids with N,N-ditosylbenzylamines

The palladium-catalyzed coupling of N,N-ditosylbenzylamines with arylboronic acids has been investigated, and the resulting diarylmethanes were obtained in high yields. Conversion of the amine to a N,N-ditosylimide group provided an efficient leaving group for the Pd-catalyzed benzylation of arylboronic acids.

A survey of the syntheses of active pharmaceutical ingredients for antiretroviral drug combinations critical to access in emerging nations

It has been roughly 25 years since the threat posed by human immunodeficiency virus type 1 (HIV-1) became widely known. The cumulative death toll from HIV/AIDS is now greater than 25 million. There are approximately 33 million people living worldwide with this disease, of whom about 68% (22.5 million) live in sub-Saharan Africa (http://www.avert.org/worldstats.htm). A number of antiretroviral (ARV) drugs have been approved for treatment of HIV/AIDS. Inhibitors of HIV reverse transcriptase (RTIs) include the nucleoside/nucleotide drugs zidovudine, lamivudine, abacavir, didanosine, stavudine, emtricitabine and tenofovir disoproxil fumarate. Non-nucleoside RTIs include nevirapine, efavirenz and etravirine. Inhibitors of HIV protease (PIs) include saquinavir, ritonavir, lopinavir, nelfinavir, indinavir, fosamprenavir and atazanavir. Enfuvirtide inhibits the HIV fusion protein. The CCR5 chemokine antagonist maraviroc and the integrase inhibitor raltegravir were very recently approved by the US FDA. Fixed-dose combinations (FDCs) have been formulated to increase tolerability, convenience and compliance. First-line drug combinations are offered to treatment-naive patients, while second-line drugs are reserved for those who no longer respond adequately to first-line therapy. In developing countries a modest but increasing fraction of those infected have access to ARVs. The Clinton HIV/AIDS Initiative estimates that 2.4 million of the nearly 8 million individuals needing treatment in developing nations have access to some drugs. First-line FDCs used in resource-poor settings are largely combinations of two nucleoside RTIs and a non-nucleoside RTI or PI. The effectiveness of these combinations decreases over time, requiring a switch to combinations that retain potency in the presence of viral resistance. Increasing access to second-line FDCs and new developments in first-line ARV therapy are cost challenges. In high-income countries the cost of ARV therapy is largely irrelevant, except for "advanced salvage" drugs such as enfuvirtide. In resource-poor settings cost is a huge factor that limits drug access, resulting in high rates of new infection and subsequent mortality. IP coverage, where granted, can keep access prices for essential ARVs higher than would otherwise be the case. Large, innovator companies have made drugs available at prices very close to the cost of manufacturing for "lowest income" countries. Generic providers in India and elsewhere provide the largest supply of drugs for the developing world. The recent issuance of Voluntary and Compulsory Licenses (VLs, CLs) through the World Trade Organization's TRIP (Treaty Respecting Intellectual Property) provisions arguably contribute to bringing down access prices. The utilization of improved science, pooled purchasing and intelligent procurement practices all definitely contribute to access. This work surveys the production processes for several critical ARVs. These are discussed in terms of scale up, raw material/intermediates and active pharmaceutical ingredient (API) costs. In some cases new routes to APIs or critical intermediates are needed. Based on potential new chemistries, there are significant opportunities to reduce cost for a number of critical ARVs.

A facile synthesis of cis-4-amino-2-cyclopentene-1-methanol, a key intermediate for the synthesis of carbocyclic nucleosides

A number of carbocyclic nucleosides can be synthesized from (+/-)-cis-4-amino-2-cyclopentene-1-methanol (3). Carbocyclic amino alcohol 3 is a key intermediate that makes possible the efficient synthesis of the carbocyclic nucleosides. In this study we wish to report an efficient synthesis of carbocyclic amino alcohol 3 from inexpensive and readily available starting material. The synthetic route employed cyclopentadiene (4) as a starting material and proceeded in 38% overall yield through 6 steps involving a hetero Diels-Alder reaction and an aza-Claisen rearrangement.

Asymmetric synthesis of carbocyclic pyrimidine nucleosides via pi-allylpalladium complex

Racemic and enantiomerically pure carbocyclic pyrimidine nucleosides were synthesized efficiently by a convergent approach using Trost nucleophilic addition of pi-allylpalladium complexes.

Versatile, diastereoselective additions of silyl ketene acetals, allyl tributylstannane, and Me(3)SiCN to N-acyl pyrazolines: asymmetric synthesis of densely functionalized pyrazolidines

We report the diastereoselective addition of a wide range of nucleophiles to chiral pyrazolines to provide facile access to a range of useful densely functionalized building blocks for asymmetric synthesis. Coupled with the asymmetric cycloaddition reaction of Me(3)SiCHN(2) to chiral acrylates, access to these chiral heterocycles is considerably expanded.

A facile synthesis of cis-9-[4-(1,2-dihydroxyethyl)-cyclopent-2-enyl]guanine and its derivative

The synthesis of carbocyclic nucleosides, cis-9-[4-(1,2-dihydroxyethyl)-cyclopent-2-enyl]guanine (3) and cis-2-amino-6-cyclopropylamino-9-[4-(1,2-dihydroxyethyl)- cyclopent-2- enyl]purine (4), was achieved from cyclopentadiene (5) in five and six steps, respectively. This route involves a hetero Diels-Alder reaction and a Pd(0)-catalyzed coupling reaction.

Efficient synthesis of carbocyclic nucleoside, (+/-)-homocarbovir via pi-allylpalladium complex formation from the allyl-N,N-ditosylimide substrate

The synthesis of a carbovir analogue, (+/-)-homocarbovir (3) was achieved from norbornadiene (4) in seven steps and 27% overall yield. This route involves a Meinwald-type rearrangement, an acid-hydrolysis of N-tosyl bicyclic enamine 5, and a Pd(0)-catalyzed coupling reaction.

The latest progress in the synthesis of carbocyclic nucleosides

This review presents the latest developments in the field of carba-nucleosides (1994-1998). Special attention is paid to the synthesis of key precursors to those carba-nucleosides that possess significant biological activities or have novel structures.