Sonia de Castro

Stereocontrolled synthesis of enantiomerically pure 2-dienyl sulfoxides via palladium-catalyzed coupling reactions☆

Abstract Enantiopure 2-sulfinyl dienes can be prepared via regio- and stereoselective hydrostannylation of alkynylsulfoxides; after conversion to the corresponding vinyliodides these substrates may be coupled with vinylstannanes via Stille methodology in the presence of BHT.

4-Benzyloxy-gamma-sultone derivatives: discovery of a novel family of non-nucleoside inhibitors of human cytomegalovirus and varicella zoster virus.

We report the synthesis and antiviral activity of a new family of non-nucleoside antivirals, derived from the 4-keto-1,2-oxathiole-2,2-dioxide (beta-keto-gamma-sultone) heterocyclic system. Several 4- and 5-substituted-5H-1,2-oxathiole-2,2-dioxide derivatives were found to have a selective inhibitory activity against human cytomegalovirus (HCMV) and varicella zoster virus (VZV) replication in vitro, being inactive against a variety of other DNA and RNA viruses. A structure-activity relationship (SAR) study showed that the presence of a benzyl at the 5 position and a benzyloxy substituent at the 4 position are a prerequisite for anti-HCMV and VZV activity. The novel compounds do not show cross-resistance against a wide variety of mutant drug-resistant HCMV strains, pointing to a novel mechanism of antiviral action.

Novel water-soluble prodrugs of acyclovir cleavable by the dipeptidyl-peptidase IV (DPP IV/CD26) enzyme

We herein report for the first time the successful use of the dipeptidyl peptidase IV (DPPIV/CD26) prodrug approach to guanine derivatives such as the antiviral acyclovir (ACV). The solution- and solid-phase synthesis of the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of acyclovir are reported. The synthesis of the demanding tetrapeptide amide prodrug of ACV 3 was first established in solution and successfully transferred onto solid support by using Ellmans dihydropyran (DHP) resin. In contrast with the valyl ester prodrug (valacyclovir, VACV), the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of ACV proved fully stable in PBS. Both prodrugs converted to VACV (for 4) or ACV (for 3) upon exposure to purified DPPIV/CD26 or human or bovine serum. Vildagliptin, a potent inhibitor of DPPIV/CD26 efficiently inhibited the DPPIV/CD26-catalysed hydrolysis reaction. Both amide and ester prodrugs of ACV showed pronounced anti-herpetic activity in cell culture and significantly improved the water solubility in comparison with the parent drug.

From β‐Amino‐γ‐sultone to Unusual Bicyclic Pyridine and Pyrazine Heterocyclic Systems: Synthesis and Cytostatic and Antiviral Activities

Herein we describe the first successful application of the β‐amino‐γ‐sultone system as an intermediate for the synthesis of hitherto virtually unknown 3H‐[1,2]‐oxathiole [4,3‐b]pyridine and pyrazine 1,1‐dioxide bicyclic heterocyclic systems. All novel compounds were evaluated for their antiviral and cytostatic activities. Compounds 3 a, 15 a, and 21 a inhibited HIV‐1‐induced cytopathicity. Compound 7 showed remarkable cytostatic activity, and can be regarded as a potential antitumor candidate for further exploration.

Synthesis of quinoxaline derivatives from substituted acetanilides through intramolecular quaternization reactions

The cyclization of 2-dialkylamino-2′-halogeno- and 2-chloro-2′-(dialkylamino)acetanilides to quinoxaline derivatives has been studied in detail. These reactions proceed, respectively, through intramolecular aromatic nucleophilic or aliphatic nucleophilic substitution reactions and depending on the substituents and the experimental conditions, they lead to 3-oxoquinoxalinium salts or, after an alkyl chloride elimination, to quinoxalin-2-ones. Some new cases of the little known intramolecular quaternization of tertiary amines with aryl halides are described.

Reactivity of the 4‐Amino‐5H‐1,2‐Oxathiole‐2,2‐Dioxide Heterocyclic System: A Combined Experimental and Theoretical Study

The reactivity of the 4-amino-5H-1,2-oxathiole-2,2-dioxide (or beta-amino-gamma-sultone) heterocyclic system has scarcely been studied. Here we describe the reactivity of this system towards electrophiles and amines on readily available model substrates differently substituted at the C-5 position. A variety of C-electrophiles, carbonyl electrophiles (such as acyl chlorides, isocyanates, or aldehydes) and halogen or nitrogen electrophiles have been explored. Both the C-3 and 4-amino positions of the beta-amino-gamma-sultone system are able to undergo electrophilic reactions, and the reaction products depend on the electrophile used and on the reaction conditions. On the other hand, nucleophilic attack of amines occurs at the C-4 position of the beta-amino-gamma-sultone system only in spiranic substrates bearing alicyclic substituents at the C-5 position. A comparative computational study between spiranic and non-spiranic substrates suggests that conformational changes, undergone on intermediate compounds, account for the observed reactivity differences. Moreover, these conformational changes seem to bring about an increase of electron density on the N-4 and C-3 atoms of the enaminic system, and a possible enhancement in the reactivity of spiranic substrates towards electrophiles in the presence of amines. Experimental data consistent with this predicted enhanced reactivity is also presented.

Design, Synthesis, and Biological Evaluation of Unconventional Aminopyrimidine, Aminopurine, and Amino‐1,3,5‐triazine Methyloxynucleosides

Herein we describe a class of unconventional nucleosides (methyloxynucleosides) that combine unconventional nucleobases such as substituted aminopyrimidines, aminopurines, or aminotriazines with unusual sugars in their structures. The allitollyl or altritollyl derivatives were pursued as ribonucleoside mimics, whereas the tetrahydrofuran analogues were pursued as their dideoxynucleoside analogues. The compounds showed poor, if any, activity against a broad range of RNA and DNA viruses, including human immunodeficiency virus (HIV). This inactivity may be due to lack of an efficient metabolic conversion into their corresponding 5′‐triphosphates and poor affinity for their target enzymes (DNA/RNA polymerases). Several compounds showed cytostatic activity against proliferating human CD4+ T‐lymphocyte CEM cells and against several other tumor cell lines, including murine leukemia L1210 and human prostate PC3, kidney CAKI‐1, and cervical carcinoma HeLa cells. A few compounds were inhibitory to Moloney murine sarcoma virus (MSV) in C3H/3T3 cell cultures, with the 2,6‐diaminotri‐O‐benzyl‐D‐allitolyl‐ and ‐D‐altritolyl pyrimidine analogues being the most potent among them. This series of unconventional nucleosides may represent a novel family of potential antiproliferative agents.

Novel Non-Nucleoside Human Cytomegalovirus Inhibitors Based Upon Tsao Nucleoside Derivatives: Structure-Activity Relationships

TSAO derivatives are a unique group of potent and highly specific inhibitors of HIV-1 replication. We have recently reported 4′-ureido TSAO derivatives that are devoid of anti-HIV-1 activity, but inhibit human cytomegalovirus with an activity comparable to that of Ganciclovir. We herein report the synthesis and biological evaluation of novel 4′-ureido TSAO derivatives in order to evaluate the structural features required for anti-HCMV activity. Interestingly, these studies revealed that the compounds may inhibit HCMV at the DNA polymerase step via a non-nucleoside mechanism.

Polypharmacology in HIV inhibition: can a drug with simultaneous action against two relevant targets be an alternative to combination therapy?

HIV infection still has a serious health and socio-economical impact and is one of the primary causes of morbidity and mortality all over the world. HIV infection and the AIDS pandemic are still matters of great concern, especially in less developed countries where the access to highly active antiretroviral therapy (HAART) is limited. Patient compliance is another serious drawback. Nowadays, HAART is the treatment of choice although it is not the panacea. Despite the fact that it suppresses viral replication at undetectable viral loads and prevents progression of HIV infection into AIDS HAART has several pitfalls, namely, long-term side-effects, drug resistance development, emergence of drug-resistant viruses, low compliance and the intolerance of some patients to these drugs. Moreover, another serious health concern is the event of co-infection with more than one pathogen at the same time (e.g. HIV and HCV, HBV, herpes viruses, etc). Currently, the multi-target drug approach has become an exciting strategy to address complex diseases and overcome drug resistance development. Such multifunctional molecules combine in their structure pharmacophores that may simultaneously interfere with multiple targets and their use may eventually be more safe and efficacious than that involving a mixture of separate molecules because of avoidance or delay of drug resistance, lower incidence of unwanted drug-drug interactions and improved compliance. In this review we focus on multifunctional molecules with dual activity against different targets of the HIV life cycle or able to block replication, not only of HIV but also of other viruses that are often co-pathogens of HIV. The different approaches are documented by selected examples.

Dipeptidyl-Peptidase IV (DPP IV/CD26)-Activated Prodrugs: A Successful Strategy for Improving Water Solubility and Oral Bioavailability

In the search of novel enzyme-based prodrug approaches to improve pharmacological properties of therapeutic drugs such as solubility and bioavailability, dipeptidyl-peptidase IV (DPP IV, also termed as CD26) enzyme activity provides a previously unexplored successful prodrug strategy. This review covers key aspects of the enzyme useful for the design of CD26-directed prodrugs. The proof-of-concept of this prodrug technology is provided for amine-containing agents by directly linking appropriate di- (or oligo)peptide moieties to a free amino group of a non-peptidic drug through an amide bond which is specifically hydrolized by DPP IV/CD26. Special emphasis is also made in discussing the design and synthesis of more elaborated tripartite prodrug systems, for further extension of the strategy to hydroxy-containing drugs. The application of this technology to improve water solubility and oral bioavailability of prominent examples of antiviral nucleosides is highlighted.