Azaphenothiazines - promising phenothiazine derivatives. An insight into nomenclature, synthesis, structure elucidation and biological properties

For the last two decades, classical phenothiazines have attracted attention of researchers, as the hitherto investigations have revealed many significant biological activities within this class of compounds, other than originally discovered neuroleptic ones. Important, new pharmaceutical results on phenothiazines, as 10-substituted dibenzothiazines, were recently highlighted in several reviews. Azaphenothiazines are structurally modified phenothiazines by substitution of one or both benzene rings in the phenothiazine ring system with the azine rings, such as: pyridine, pyridazine, pyrimidine, pyrazine, 1,2,4-triazine, quinoline, quinoxaline, benzoxazine and benzothiazine. They form over 50 different heterocyclic systems, of tri-, tetra-, penta- and hexacyclic structures, and contain from one to even four azine nitrogen atoms. This review summarizes the methodical knowledge on azaphenothiazines, referring to their nomenclature, synthesis, structure analysis and above all significant varied biological activities, examined in vitro and in vivo. It describes, in addition, current trends in the synthesis of azaphenothiazines. The influence of the azaphenothiazine ring system, the nature of the substituents, predominantly at the thiazine nitrogen atom, as well as at the azine nitrogen atom and carbon atom, on the biological activities, were also discussed.

Synthesis and anticancer and lipophilic properties of 10-dialkylaminobutynyl derivatives of 1,8- and 2,7-diazaphenothiazines

New derivatives of two isomeric types of azaphenothiazines, 1,8- and 2,7-diazaphenothiazine, containing the triple bond substituents and additionally tertiary cyclic and acyclic amine groups, were synthesized and tested for their anticancer activity. The compounds exhibited differential inhibitory activities. Better results were obtained when the acetylenic group was transformed via the Mannich reaction to the dialkylaminobutynyl groups. The most active was 2,7-diazaphenothiazine with the N-methylpiperazine-2-butynyl substituent against the human ductal breast epithelial tumor cell line T47D, more potent than cisplatin. The 2,7-diazaphenothiazine system turned out to be more active than isomeric 1,8-diaza one. For the most active compound, the expression of TP53, CDKN1A, BCL-2 and BAX genes was detected by the RT-QPCR method. The gene expression ratio BACL-2/BAX suggests the mitochondrial apoptosis in T47D cells. The synthesis makes possible to obtain many new bioactive phenothiazines with the dialkylaminoalkynyl substituents inserting various tertiary cyclic and acyclic amine moieties to the substituents.

6-Substituted 9-fluoroquino[3,2-b]benzo[1,4]thiazines display strong antiproliferative and antitumor properties

6-Substituted 9-fluoroquino[3,2-b]benzo[1,4]thiazines - a new type of tetracyclic azaphenothiazines-were obtained from of 6H-9-fluoroquinobenzothiazine by the introduction of appropriate substituents to the thiazine nitrogen atom (alkyl, aminoalkyl, amidoalkyl, sulfonamidoalkyl and nitrogen half-mustard groups). The compounds displayed differential cytotoxic as well as antiproliferative actions against human peripheral blood mononuclear cells (PBMC) stimulated with phytohemagglutinin A (PHA). In addition, they suppressed lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-α) production by whole blood human cell cultures. Two compounds (4 and 15, with the propargyl and methanesulfonamidopropyl groups) were selected for further experiments because of lack of cytotoxicity and strong antiproliferative actions. Compound 4 showed strong suppressive actions on growth of L1210, SW948, A-431 and CX-1 tumor cell lines which were close to those of cisplatin, the reference drug (e.g. GI50 of 2.28 μg/mL vs. 1.86 μg/mL for L1210 cells). Further, the compound appeared to be equally effective as cyclosporine A (CsA) in the inhibition of human two-way mixed lymphocyte reaction (MLR). The compound did not significantly inhibit interleukin 2 (IL-2)-induced growth of CTLL-2 cell line. In addition, inhibition of prostaglandin (PG) synthesis by indomethacin or block of PG receptors did not interfere with the inhibitory effect of the compound on PHA-induced cell proliferation. Therefore, it is likely that the compound acts by inhibiting cell cycle as proposed for other phenothiazines. Further studies are required for the elucidation of the mechanism of action and therapeutic utility of these compounds in more advanced in vivo models.

Estimation of the lipophilicity of new anticancer and immunosuppressive 1,8-diazaphenothiazine derivatives

The lipophilicity of anticancer and immunosuppressant active 1,8-diazaphenothiazine derivatives ( 1: - 16: ) has been investigated. Their lipophilicity (RM0 and log PTLC) was determined by reversed-phase thin-layer chromatography with mixtures of acetone and TRIS buffer as mobile phases. The parameter RM0 and specific hydrophobic surface area b were significantly intercorrelated showing congeneric classes of dipyridothiazines. The parameter RM0 was discussed in the terms of the structure-lipophilicity relationships and transformed into parameter log PTLC by use of the calibration curve. The lipophilicity was correlated with molecular and biomolecular descriptors (human intestinal absorption, blood-brain barrier, plasma protein binding, MDCK) and in vitro tumor necrosis factor alpha inhibition and antiproliferative activity.

Antioxidant activity of newly synthesized 2,7-diazaphenothiazines

A series of 19 derivatives of 2,7-diazaphenothiazine was synthesized and evaluated for their antioxidant activity bearing in mind the structural similarity with "classical" phenothiazines several of which are considered powerful antioxidants. Among the new derivatives that inhibited in vitro Fe(2+)/ascorbate-induced lipid peroxidation of rat liver microsomal membranes, several exhibited significant antioxidant activity with IC(50 )values in the range of 64-125 microM. Although N-substitution led to a variable degree of antioxidant activity, the latter appears to correlate with the lipophilicity (expressed as clogP values) of the substituted derivatives. Reduced lipophilicity may also explain the relatively lower protection offered by these derivatives against lipid peroxidation when compared to their "classical" phenothiazine counterparts. Thus, modification of the phenothiazine structure by a substitution of two benzene rings with pyridine rings to form this new type of azaphenothiazines does not enhance antioxidant activity, although it retains it.