Andrey A. Berezin

A magnetostructural investigation of an abrupt spin transition for 1-phenyl-3-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl

1-Phenyl-3-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl is the first example of a hydrazyl radical that shows a reversible sharp spin transition fully completed within 5(1) K. The nominally first-order transition takes place at ca. 58(2) K and proceeds via subtle changes of intra- and interstack interactions between two similar structural phases. The low-temperature phase (5-60 K) is diamagnetic and has a singlet ground state (2Jexp = -166.8 cm(-1), gsolid = 2.0042, ρ = 0.2%) stemming from a multicenter two-electron interaction. The high-temperature phase (60-300 K) is paramagnetic as a result of noninteracting S = 1/2 spins arising from weakly bound dimers.

Design, synthesis and biological evaluation of benzo[e][1,2,4]triazin-7(1H)-one and [1,2,4]-triazino[5,6,1-jk]carbazol-6-one derivatives as dual inhibitors of beta-amyloid aggregation and acetyl/butyryl cholinesterase

Alzheimers disease (AD) onset and progression are associated with the dysregulation of multiple and complex physiological processes and a successful therapeutic approach should therefore address more than one target. Two new chemical entities, the easily accessible heterocyclic scaffolds 1,3-diphenylbenzo[e][1,2,4]triazin-7(1H)-one (benzotriazinone I) and 2-phenyl-6H-[1,2,4]triazino[5,6,1-jk]carbazol-6-one (triazafluoranthenone II), were explored for their multitarget-directed inhibition of beta-amyloid (Aβ) fibrillization and acetyl- (AChE) and/or butyryl- (BChE) cholinesterase, three valuable targets for AD therapy. Introduction of appropriate amine substituents at positions 6 and 5 on scaffold I and II, respectively, allowed the preparation of a series of compounds that were tested as Aβ(1-40) aggregation and cholinesterase inhibitors. Potent inhibitors of Aβ self-aggregation were discovered and among them benzotriazinone 7 exhibited an outstanding IC(50) equal to 0.37 μM. Compounds bearing a basic amine linked to the heterocyclic scaffold through a linear alkyl chain of varying length also afforded good ChE inhibitors. In particular, benzotriazinone 24 and triazafluoranthenone 38 were endowed with an interesting multiple activity, the former displaying IC(50) values of 1.4, 1.5 and 1.9 μM on Aβ aggregation and AChE and BChE inhibition, respectively, and the latter showing IC(50) values of 1.4 and an outstanding 0.025 μM in the Aβ aggregation and BChE inhibition, respectively. Benzotriazinone 24 and triazafluoranthenone 29, selected owing to their suitable aqueous solubility and Aβ aggregation inhibition, were submitted to a time course kinetic assay followed with thioflavin T (ThT) spectrofluorimetry, circular dichroism (CD) and transmission electron microscopy (TEM). Experimental data indicated that 24 acted at a low concentration ratio (10 μM 24 vs. 50 μM Aβ), stabilizing the unstructured Aβ peptide and inhibiting fibrillogenesis, and that 29 also acted as fibrillization inhibitor, but likely enhancing and stabilizing the β-sheet arrangement of Aβ to yield protofibrillar species as detected by TEM.

Effective exchange coupling in alternating-chains of a π-extended 1,2,4-benzotriazin-4-yl

Air stable 1,3,7-triphenyl-1,4-dihydrothiazolo[5′,4′:4,5]benzo[1,2-e][1,2,4]triazin-4-yl packs in 1D π stacks made of radical pairs with alternate short and long interplanar distances. The magnetic susceptibility exhibits a broad maximum at 73 ± 5 K and is interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with an average exchange interaction of J = −43.8 cm−1 and an alternation parameter α = 0.3 (gsolid = 2.0028). The enhanced overlap between the π-extended SOMO orbitals leads to strong antiferromagnetic interactions along the chains (J1 = −87.6 cm−1 and J2 = −26.3 cm−1).

Tetraphenylhexaazaanthracenes: 16π Weakly Antiaromatic Species with Singlet Ground States

Tetraphenylhexaazaanthracene, TPHA-1, is a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state. TPHA-1 overcomes its weak 16π antiaromaticity by partitioning its π system into 6π positive and 10π negative cyanines. The synthesis of TPHA-1 is low yielding and accompanied by two analogous TPHA isomers: the deep red, non-charge-separated, quinoidal TPHA-2, and the deep green TPHA-3 that partitions into two equal but oppositely charged 8π cyanines. The three TPHA isomers are compared.

Preparation of Blatter Radicals via Aza-Wittig Chemistry: The Reaction of N-Aryliminophosphoranes with 1-(Het)aroyl-2-aryldiazenes

Reacting N-aryliminophosphoranes with 1-(het)aroyl-2-aryldiazenes in preheated diphenyl ether at ca. 150-250 °C for 5-25 min affords in most cases the 1,3-diaryl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yls (aka Blatter radicals) in moderate to good yields. All new compounds are fully characterized, including EPR and CV studies for the radicals. Single-crystal X-ray structures of 1-benzoyl-2-(perfluorophenyl)diazene and 1-(perfluorophenyl)-3-phenyl-1,4-dihydrobenzo[e][1,2,4]triazinyl are also presented.

Discovery of anti-cancer activity for benzo[1,2,4]triazin-7-ones: Very strong correlation to pleurotin and thioredoxin reductase inhibition.

The thioredoxin (Trx)-thioredoxin reductase (TrxR) system plays a key role in maintaining the cellular redox balance with Trx being over-expressed in a number of cancers. Inhibition of TrxR is an important strategy for anti-cancer drug discovery. The natural product pleurotin is a well-known irreversible inhibitor of TrxR. The cytotoxicity data for benzo[1,2,4]triazin-7-ones showed very strong correlation (Pearson correlation coefficients ∼0.8) to pleurotin using National Cancer Institute COMPARE analysis. A new 3-CF3 substituted benzo[1,2,4]triazin-7-one gave submicromolar inhibition of TrxR, although the parent compound 1,3-diphenylbenzo[1,2,4]triazin-7-one was more cytotoxic against cancer cell lines. Benzo[1,2,4]triazin-7-ones exhibited different types of reversible inhibition of TrxR, and cyclic voltammetry showed characteristic quasi-reversible redox processes. Cell viability studies indicated strong dependence of cytotoxicity on substitution at the 6-position of the 1,3-diphenylbenzo[1,2,4]triazin-7-one ring.

The Suppression of Columnar π-Stacking in 3-Adamantyl-1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl

3-Adamantyl-1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (4) crystallizes as chains of radicals where the spin bearing benzotriazinyl moieties are isolated from each other. Magnetic susceptibility studies in the 5–300 K temperature region indicate that radical 4 demonstrates typical paramagnetic behavior stemming from non-interacting S = ½ spins.

Correction to Route to Benzo- and Pyrido-Fused 1,2,4-Triazinyl Radicals via N′-(Het)aryl-N′-[2-nitro(het)aryl]hydrazides

As such, Scheme 7 in the original article should now be as follows: Furthermore, the Experimental Section (section 4.7.2) now becomes: 4.7.2. 5-[1,3-Di(pyrid-2-yl)-7-(tri f luoromethyl)-1,4dihydrobenzo[e][1,2,4]triazin-4-yl]-1,3-di(pyrid-2-yl)-7-(trif luoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1o). To a stirred solution of 1,3-di(pyrid-2-yl)-7-(trifluoromethyl)-1,4-dihydro1,2,4-benzotriazine (23c) (355 mg, 1.0 mmol) in DCM (10 mL) at ca. 20 °C was added MnO2 (869 mg, 10.0 mmol). After 2 days, the reaction mixture was filtered through Celite and rinsed with additional DCM, and volatiles were removed in vacuo. The residue was chromatographed on basic alumina (DCM/t-BuOMe, 1:1) to give the title compound 1o (173 mg, 49%) as black needles. Mp (DSC) onset 218.1 °C, peak max 222.9 °C (from MeCN); Rf 0.49 (Al2O3, DCM); (found C, 60.93; H, 3.07; N, 19.89. C36H21F6N10• requires C, 61.11; H, 2.99; N, 19.79%); λmax(DCM)/nm 236 (log ε 4.56), 267 (4.66), 282 inf (4.63), 328 inf (4.36), 436 (3.78), 510 (3.31); νmax/cm −1 3061w and 3011w (Ar CH), 1585m, 1568w, 1514w, 1466m, 1429s, 1402m, 1375m, 1344s, 1325s, 1290m, 1271s, 1233w, 1190w, 1161s, 1115s, 1088m, 1061m, 1043w, 991w, 947w, 912m, 878m, 822m, 800m, 775m, 743m, 733w; MALDITOF (m/z) 709 (MH + 1, 39%), 708 (MH, 100), 696 (24), 630 (8), 617 (20), 603 (9), 588 (17), 354 (8), 342 (9), 339 (6). The structures of the remaining radicals have been rechecked, and their structures are correct. From a brief initial study, it appears that the higher basicity of the dipyridyl 1o is partly responsible for this unexpected dimerization, and we have been unable to find conditions to oxidize the precursor triazine 23c that do not give the dimeric species 1o. This dimerization is now under study, and we plan to provide a full report on this reaction in the very near future.

Anti-Cancer Activity of Phenyl and Pyrid-2-yl 1,3-Substituted Benzo[1,2,4]triazin-7-ones and Stable Free Radical Precursors

Cell viability studies for benzo[1,2,4]triazin-7-ones and 1,2,4-benzotriazinyl (Blatter-type) radical precursors are described with comparisons made with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). All of the stable free radicals were several orders of magnitude less cytotoxic than the benzo[1,2,4]triazin-7-ones. The synthesis and evaluation of two new pyrid-2-yl benzo[1,2,4]triazin-7-ones are described, where altering the 1,3-substitution from phenyl to pyrid-2-yl increased cytotoxicity against most cancer cell lines, as indicated using National Cancer Institute (NCI) one-dose testing. COMPARE analysis of five-dose testing data from the NCI showed very strong correlations to the naturally occurring anti-cancer compound pleurotin. COMPARE is program, which analyzes similarities in cytotoxicity data of compounds, and enables quantitative expression as Pearson correlation coefficients. Compounds were also evaluated using the independent MTT assay, which was compared with SRB assay data generated at the NCI.

Tailored Synthesis of N-Substituted peri-Xanthenoxanthene Diimide (PXXDI) and Monoimide (PXXMI) Scaffolds

The tailored synthesis of homo (A2) and hetero (AB) N-substituted peri-xanthenoxanthene diimides (PXXDIs) and peri-functionalized PXX monoimides (PXXMIs) from 3-hydroxy naphthalic anhydride is described. As A2-type PXXDIs could be synthesized in one step, AB-type PXXDIs and PXXMIs were prepared through a modular approach capitalizing on sequential Suzuki coupling, imidation, and Pummerer reactions with very high yields. In view of their potential applications as organic semiconductors, self-organization studies were performed through liquid deposition on surfaces, depicting the formation of islands, needles, and rods.