Chemoenzymatic Asymmetric Total Synthesis of Phosphodiesterase Inhibitors: Preparation of a Polycyclic Pyrazolo[3,4-d]pyrimidine from an Acylnitroso Diels−Alder Cycloadduct-Derived Aminocyclopentenol

A Highly Stereospecific Claisen-Sakurai Approach to Densely Functionalized Cyclopentenols

The formation of highly substituted cyclopentenols was developed using a Claisen-Sakurai reaction. Both elements of the reaction can be performed in a one-pot sequence that provides the corresponding cyclized products in high stereoselectivity. The stereochemical outcome is defined by a combination of Claisen stereospecificity and stereoelectronic effects in the Sakurai cyclization that promotes reactivity via an anti-S_E' antiperiplanar transition state. This was determined by examination of the product stereochemistry and through detailed DFT analysis.

Stereoselective Synthesis of Isoxazolidines via Copper-Catalyzed Alkene Diamination

A convenient copper-catalyzed intramolecular/intermolecular alkene diamination reaction to synthesize 3-aminomethyl-functionalized isoxazolidines under mild reaction conditions and with generally high levels of diastereoselectivity was achieved. This reaction demonstrates that previously underutilized unsaturated carbamates are good [Cu]-catalyzed diamination substrates. Sulfonamides, anilines, benzamide, morpholine, and piperidine can serve as the external amine source. This relatively broad amine range is attributed to the mild reaction conditions. Reduction of the N-O bond could also be achieved, revealing the corresponding 3,4-diamino-1-alcohols efficiently.

Generation and Trapping of Nitrosocarbonyl Intermediates

The nitrosocarbonyls (R-CONO) are highly reactive species and remarkable intermediates toward different synthetic targets. This review will cover a research area whose impact in current organic synthesis is constantly increasing in the chemical community. This review represents the first and comprehensive picture on the generation and trapping of nitrosocarbonyls and is solidly built on more than 380 papers. Six different classes of key starting materials such as hydroxamic acids, N-hydroxy carbamates, N-hydroxyureas, nitrile oxides, and 1,2,4-oxadiazole-4-oxides were highlighted. The content of the review surveys all the methods to generate the nitrosocarbonyls through different approaches (oxidative, thermal, photochemical, catalytic, aerobic, and the less common ones) in the light of efficiency, yields, and mildness. The most successful trapping agents employed to catch these fleeting intermediates are reviewed, exploiting their superior dienophilic, enophilic, and electrophilic power. The work is completed by paragraphs dedicated to the detection of the intermediates, theoretical studies, and insights about the challenges and future directions for the field.

Isatin-pyrazole benzenesulfonamide hybrids potently inhibit tumor-associated carbonic anhydrase isoforms IX and XII

New series of benzenesulfonamide derivatives incorporating pyrazole and isatin moieties were prepared using celecoxib as lead molecule. Biological evaluation of the target compounds was performed against the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more precisely against the human isoforms hCA I, II (cytosolic), IX and XII (transmembrane, tumor-associated enzymes). Most of the tested compounds efficiently inhibited hCA I, II and IX, with KIs of 2.5-102 nM, being more effective than the reference drug acetazolamide. Compounds 11e, 11f, 16e and 16f were found to inhibit hCA XII with Ki of 3.7, 6.5, 5.4 and 7.2 nM, respectively. Compounds 11e and 16e, with 5-NO2 substitution on the isatin ring, were found to be selective inhibitors of hCA IX and hCA XII. Docking studies revealed that the NO2 group of both compounds participate in interactions with Asp132 within the hCA IX active site, and with residues Lys67 and Asp130 in hCA XII, respectively.

Asymmetric synthesis of cis-aminocyclopentenols, building blocks for medicinal chemistry

A highly efficient one-pot multistep process involving an asymmetric Pd(II)-catalyzed Overman rearrangement and a Ru(II)-catalyzed ring-closing metathesis reaction has been developed for the preparation of (R)- or (S)-aminocyclopenta-2-enes. The rapid strategy employed and the relatively mild conditions of the one-pot process allowed the multigram synthesis of the carbocycles in high enantiomeric excess (92% ee). The synthetic utility of these compounds was demonstrated by the stereoselective incorporation of hydroxyl groups, generating cis-4- and cis-5-aminocyclopenta-2-en-1-ols, important building blocks for medicinal chemistry.

The nitrosocarbonyl hetero-Diels-Alder reaction as a useful tool for organic syntheses

Organic transformations that result in the formation of multiple covalent bonds within the same reaction are some of the most powerful tools in synthetic organic chemistry. Nitrosocarbonyl hetero-Diels-Alder (HDA) reactions allow for the simultaneous stereospecific introduction of carbon-nitrogen and carbon-oxygen bonds in one synthetic step, and provide direct access to 3,6-dihydro-1,2-oxazines. This Review describes the development of the nitrosocarbonyl HDA reaction and the utility of the resulting oxazine ring in the synthesis of a variety of important, biologically active molecules.

A facile one-pot synthesis of 1-arylpyrazolo[3,4-d]pyrimidin-4-ones

One pot synthesis of 1-arylpyrazolo[3,4-d]pyrimidin-4-ones by the reaction of 5-amino-N-substituted-1H-pyrazole-4-carbonitrile with different lower aliphatic acids in the presence of POCl(3) has been developed. The structures of all the title compounds have been confirmed by IR, (1)H-NMR, (13)CNMR, and elemental analyses. Moreover, the structures of one of these compounds, 2c, was confirmed by single-crystal X-ray diffraction.

Synthesis and anticancer activity of new hydroxamic acid containing 1,4-benzodiazepines

By employing an intramolecular Pd(0)-mediated ring opening of an acylnitroso-derived cycloadduct, new hydroxamic acid containing benzodiazepines have been synthesized and have demonstrated biological activity in MCF-7 and PC-3 tumor cell lines. Subsequent N-O bond reduction of the hydroxamate has provided access to amide analogues for SAR studies. During the course of our syntheses, an intermediate oxazoline N-oxide was isolated and gave insight into the mechanism of the key Pd(0)-mediated reaction.

Syntheses of new spirocarbocyclic nucleoside analogs using iminonitroso Diels-Alder reactions

N-Cbz- and Boc-protected spirocyclic dienes were prepared by dialkylation of cyclopentadiene. These dienes coupled efficiently in a series of iminonitroso Diels-Alder reactions to produce a series of new spirocyclic adducts. Hydrogenolysis of these adducts afforded new spirocycles that contain multiple handles for further functionalization. Furthermore, stereocontrolled dihydroxylation and reductive cleavage of the spirocyclic adducts generated versatile scaffolds for the syntheses and derivatization of novel spirocyclic carbocyclic nucleoside analogs.

Substrate-dependent dihydroxylation of substituted cyclopentenes: toward the syntheses of carbocyclic sinefungin and noraristeromycin

Carbocyclic nucleosides are of considerable interest for the development of new therapeutic agents. A key reaction in the preparation of many such nucleoside analogues is dihydroxylation of appropriately substituted cyclopentenes. Although often considered a routine reaction, in this paper, we report the dramatic influence of substituents on the facial selectivity of dihydroxylations. The substituted cyclopentene substrates are derived from acylnitroso cycloaddition reactions of cyclopentadiene, followed by N-O reduction and efficient enzymatic resolution. The results are directly utilized in a very efficient asymmetric synthesis of an antiviral carbocyclic nucleoside, noraristeromycin 5. Extensions toward the synthesis of carbocyclic sinefungin 7 document the importance of realizing the substituent dependence of the dihydroxylation reaction.

Reactions of nitroso hetero-Diels-Alder cycloadducts with azides: stereoselective formation of triazolines and aziridines

The addition of azides to acylnitroso hetero-Diels-Alder cycloadducts derived from cyclopentadiene affords exo-triazolines in excellent yield. The reaction is greatly affected by the level of alkene strain, while sterically demanding azides do not hinder the reaction. Conversion of the triazolines to aziridines is also described.

Stereoselective Total Synthesis of (+)-Streptazolin by Using a Temporary Silicon-Tethered RCM Strategy

A stereoselective total synthesis of (+)-streptazolin 1 was accomplished starting from readily available aminocyclopentenol (-)-7. The synthetic sequence highlights an intramolecular aldol condensation strategy to construct the piperidine core and a silicon-tethered ring-closing metathesis strategy to install the Z exocyclic ethylidene side chain of streptazolin. Separate protodesilylation and Tamao oxidation of a common intermediate 32 afforded streptazolin and the precursor for 13-hydroxystreptazolin. The overall yield for (+)-streptazolin 1 from aminocyclopentenol (-)-7 was 4.8% for a total of 16 steps.