Nitrogen Protecting Groups: Recent Developments and New Applications

Structural Identification between Phthalazine-1,4-Diones and N-Aminophthalimides via Vilsmeier Reaction: Nitrogen Cyclization and Tautomerization Study

N-Aminophthalimides and phthalazine 1,4-diones were synthesized from isobenzofuran-1,3-dione, isoindoline-1,3-dione, furo [3,4-b] pyrazine-5,7-dione, or 1H-pyrrolo [3,4-c] pyridine-1,3-dione with monohydrate hydrazine to carry out the 5-exo or 6-endo nitrogen cyclization under the different reaction conditions. Based on the control experimental results, 6-endo thermodynamic hydrohydrazination and kinetical 5-exo cyclization reactions were individually selective formation. Subsequently, Vilsmeier amidination derivatization was successfully developed to probe the structural divergence between N-aminophthalimide 2 and phthalazine 1,4-dione 3. On the other hand, the best tautomerization of N-aminophthalimide to diazinone was also determined under acetic acid mediated solution.

Crystal structure of methyl (1-phenylethyl)carbamate, C10H13NO2

C10H13NO2, monoclinic, P21 (no. 14), a = 9.9882(7) Å, b = 8.5202(6) Å, c = 23.1403(18) Å, β = 91.010(2)°, V = 1969.0(2) Å3, Z = 8, R gt(F) = 0.0387, wR ref(F 2) = 0.0919, T = 173(2)K.

Highly selective acylation of polyamines and aminoglycosides by 5-acyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-ones

5-Acyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-ones, accessible from arylpropargyl phenyldiazoacetates, are highly selective acyl transfer reagents for di- and polyamines, as well as aminoalcohols and aminothiols. As reagents with a carbon-based leaving group, they have been applied for benzoyl transfer with a broad selection of substrates containing aliphatic amino in combination with other competing nucleophilic functional groups. The substrate scope and levels of selectivity for direct benzoyl transfer exceed those of known benzoylating reagents. With exceptional selectivity for acylation between primary amines bound to primary and secondary carbons, these new reagents have been used in direct site-selective monobenzoylation of aminoglycoside antibiotics.

Aromatic Chlorosulfonylation by Photoredox Catalysis

Visible-light photoredox catalysis enables the efficient synthesis of arenesulfonyl chlorides from anilines. The new protocol involves the convenient in situ preparation of arenediazonium salts (from anilines) and the reactive gases SO₂ and HCl (from aqueous SOCl₂ ). The photocatalytic chlorosulfonylation operates at mild conditions (room temperature, acetonitrile/water) with low catalyst loading. Various functional groups are tolerated (e.g., halides, azides, nitro groups, CF₃ , SF₅ , esters, heteroarenes). Theoretical and experimental studies support a photoredox-catalysis mechanism.

Integration of oxidative arylation with sulfonyl migration: one-pot tandem synthesis of densely functionalized (NH)-pyrroles

A one-pot synthesis of 2-aryl-3-alkyl/aryl-sulfonyl-(NH)-pyrroles from N-sulfonylpyrroles, developed for the first time, via palladium-catalyzed oxidative C-2 arylation followed by sulfonyl migration is described.

Selective Protection of Secondary Amines as the N-Phenyltriazenes. Application to Aminoglycoside Antibiotics

Selective protection of secondary amines as triazenes in the presence of multiple primary amines is demonstrated, with subsequent protection of the primary amines as either azides or carbamates in the same pot. Aminoglycoside antibiotic examples reveal broad functional group compatibility. The triazene group is removed with trifluoroacetic acid and, because of the low barrier to rotation, affords sharp (1)H NMR spectra at room temperature.

Metal-free TBHP-mediated oxidative ring openings of 2-arylimidazopyridines via regioselective cleavage of C–C and C–N bonds

A highly regioselective TBHP-mediated ring opening of imidazopyridinesviacleavage of C–C and C–N bonds has been realized for the first time to afford usefulN-(pyridin-2-yl)benzamides under mild conditions.

The cathepsin B inhibitor, z-FA-CMK is toxic and readily induced cell death in human T lymphocytes

The cathepsin B inhibitor, benzyloxycarbonyl-phenylalanine-alanine-chloromethylketone (z-FA-CMK) was found to be toxic and readily induced cell death in the human T cell line, Jurkat, whereas two other analogs benzyloxycarbonyl-phenylalanine-alanine-fluoromethylketone (z-FA-FMK) and benzyloxycarbonyl-phenylalanine-alanine-diazomethylketone (z-FA-DMK) were not toxic. The toxicity of z-FA-CMK requires not only the CMK group, but also the presence of alanine in the P1 position and the benzyloxycarbonyl group at the N-terminal. Dose-response studies showed that lower concentrations of z-FA-CMK induced apoptosis in Jurkat T cells whereas higher concentrations induced necrosis. In z-FA-CMK-induced apoptosis, both initiator caspases (-8 and -9) and effector caspases (-3, -6 and -7) were processed to their respective subunits in Jurkat T cells. However, only the pro-form of the initiator caspases were reduced in z-FA-CMK-induced necrosis and no respective subunits were apparent. The caspase inihibitor benzyloxycarbonyl-valine-alanine-aspartic acid-(O-methyl)-fluoromehylketone (z-VAD-FMK) inhibits apoptosis and caspase processing in Jurkat T cells treated with low concentration of z-FA-CMK but has no effect on z-FA-CMK-induced necrosis and the loss of initiator caspases. This suggests that the loss of initiator caspases in Jurkat T cells during z-FA-CMK-induced necrosis is not a caspase-dependent process. Taken together, we have demonstrated that z-FA-CMK is toxic to Jurkat T cells and induces apoptosis at low concentrations, while at higher concentrations the cells die of necrosis.

Iodine-Mediated Neutral and SelectiveN-Boc Deprotection

A simple, efficient, and alternative method has been developed for theN-Boc deprotection of structurally diverse protected amines. Selective removal ofN-Boc groups was achieved with excellent yields under a solvent-free condition or in a solvent using iodine as a catalyst. The methodology involving the first use of iodine forN-Boc deprotection of protected amines represents an effective and useful alternative to the previously reported methods.

Microwave Assisted Synthesis of Sodium Sulfonates Precursors of Sulfonyl Chlorides and Fluorides

We describe the use of a microwave reaction for the conversion of various bromides to sodium sulfonates that have been further elaborated to sulfonyl chlorides. This new approach leads to much improved yields and shorter reaction times. Representative sulfonyl chlorides serve as precursors for the respective sulfonyl fluorides that are potent inhibitors of the fatty acid amide hydrolase.

Chlorotrimethylsilane−Nitrate Salts as Oxidants: Direct Oxidative Conversion of Thiols and Disulfides to Sulfonyl Chlorides

A mixture of nitrate salt and chlorotrimethylsilane is found to be a mild and efficient reagent for the direct oxidative conversion of thiols (1) and disulfides (2) to the corresponding sulfonyl chlorides (3) in excellent yields through oxidative chlorination. Sulfides and sulfoxides were also found to undergo oxidation to sulfones under similar reaction conditions. In most cases these reactions are highly selective, simple, and clean, affording products in high yield and purity.

Dinuclear Zinc-Catalyzed Enantioselective Aza-Henry Reaction

The dinuclear zinc catalyst 1a was found to catalyze the addition of nitroalkanes to carbamate-protected imines. This aza-Henry reaction proceeds with high enantioselectivity when various carbamate-protected imines are used. alpha,beta-Unsaturated imines proved to be a particularly useful class of substrate routinely giving the alpha-nitro amine products in high enantiomeric excess.

Catalyst-Free Chemoselective N-tert-Butyloxycarbonylation of Amines in Water

[Structure: see text] Catalyst-free N-tert-butyloxycarbonylation of amines in water is reported. The N-t-Boc derivatives were formed chemoselectively without any isocyanate, urea, N,N-di-t-Boc, and O/S-t-Boc as side products. Chiral amines, esters of alpha-amino acids, and beta-amino alcohol afforded optically pure N-t-Boc derivatives. Amino alcohol and 2-aminophenol afforded the N-t-Boc derivative without oxazolidinone formation. Selectivity was observed during competition of aromatic amine vs aliphatic amine, amine vs amino acid ester, amine vs amino alcohol, and primary amine vs secondary amine.

HClO4–SiO2as a new, highly efficient, inexpensive and reusable catalyst for N-tert-butoxycarbonylation of amines

Perchloric acid adsorbed on silica-gel (HClO4-SiO2) was found to be a new, highly efficient, inexpensive and reusable catalyst for chemoselective N-tert-butoxycarbonylation of amines at room temperature and under solvent-free conditions.

The Bis(trimethylsilyl)methyl Group as an Effective N-Protecting Group and Site-Selective Control Element in Rhodium(II)-Catalyzed Reaction of Diazoamides

The intramolecular rhodium(II)-carbenoid-mediated C-H insertion reaction of structurally varied N-bis(trimethylsilyl)methyl,N-substituted diazoamides is studied. It has been found that in tertiary diazoamides the N-bis(trimethylsilyl)methyl (N-BTMSM) group is effective for conformational control about the amide N-C(O) bond; C-H insertion occurs at the other N-substituent. In C(alpha)-branched diazoamides, the N-BTMSM is found also to exert its influence on the conformational preference about the N-C(alpha) bond, which affects the regioselectivity of the C-H insertion in these systems. In unbranched diazoamides, inherent electronic effects of the N-substituent affect the regio- and chemoselectivity of the reaction; however, in branched diazoamides, electronic effects of the N-substituent and the alpha-substituent at the carbenoid carbon are subtle, but important in the deciding the eventual outcome of the reaction.

Comparative in vivo behavior studies of cyclen-based copper-64 complexes: regioselective synthesis, X-ray structure, radiochemistry, log P, and biodistribution

The in vivo behavior of copper(II)-cyclen complexes was modified via substitution of the parent ligand with two different substituents, 4-tert-butylbenzyl and acetate. This was achieved by using same synthetic strategy (regioselective protection/first alkylation/deprotection/second alkylation) to give nine cyclen derivatives. The X-ray structure of [Cu(2c)Cl]+ (2c = 1-(4-tert-butylbenzyl)-1,4,7,10-tetraazacyclododecane) showed that the chlorine ion from the reaction mixture occupied the remaining apical position of a square pyramidal coordination environment of these Cu-cyclen complexes. Eight out of nine compounds were labeled with 64Cu in high radiochemical purity. log P measurements showed that the lipophilicities of the copper complexes were increased dramatically by attaching hydrophobic substituents on the nitrogen atoms of cyclen. Conversely, as the number of acetate groups increased, the lipophilicity was decreased. The biodistribution of Cu-cyclen complexes was found to be influenced mostly by the overall charge of the complexes rather than their lipophilicity. Positively charged (+2) complexes showed high blood retention at early time points with sluggish clearance from liver by 24 h. The attachment of even one acetate group onto cyclen accelerated blood and liver clearance dramatically compared to +2 charged Cu(II) complexes. Neutral trans-substituted Cu-4 showed the best clearance and lowest retention of doses from all organs most time, followed by -1 charged complex Cu-2. Trans-substituted complexes structure isomers Cu-3 and Cu-4 showed better clearance and lower retention from all organs than their cis-counterparts Cu-5 and Cu-6.