supplementary materials

The search for new antiviral and antibacterial compounds has accelerated in recent years due to the prevalence of antibiotic resistance. Thus, in the development of antibiotics as well as anticancer drugs, attention has been drawn towards a series of new targets, one of these being regulation of cell growth at the DNA/RNA level. A large group of antibiotics affect protein synthesis or nucleic acid metabolism, for example, via interference with DNA replication, DNA transcription, aminoacyl-tRNA formation or RNA translation. Intercalation, that is formation of a non-covalent complex of the drug with the duplex DNA, will result in inhibition of DNA replication and/or transcription, presumably due to deformation of double helix. Many intercalating drugs contain planar aromatic ring systems with cationic moieties. In the 80t h, a group of potential antibiotics containing the planar tricyclic heteroaromatic phenazine was isolated (Geiger et al., 1988) and since then, a number of phenazine carboxylic acids have been synthesized showing significant antimicrobial activity towards a broad range of bacteria (Bahnmüller et al., 1988; Laursen et al., 2002).

In general, natural and synthetic phenazines have attracted considerable attention because of their interesting biological activities. Benzo[a]phenazine derivatives have been considered efficient DNA intercalating ligands, with antitumor activity in leukaemia and solid tumors(Rewcastle et al., 1987). They also show broad-spectrum antibiotic activity (Emoto et al., 2000), antimalarial (Mackgatho et al., 2000; Andrade-Neto et al., 2004), anti-hepatitis C viral replication (Wang et al., 2000).

More specifically, tetramethylpiperidine (TMP)-substituted phenazines were assayed against Mycobacterium tuberculosis H37Rv (ATCC 27294) and some of them were significantly more active than clofazimine, including multidrug-resistant clinical strains of this microbial pathogen (Van Rensburg et al., 2000).

Tuberculosis is one of the most devastating bacterial disease having high rates of morbidity and mortality. M. tuberculosis invades the host immune system and persists in pulmonary granulomas (Agrawal et al., 2007). As resistant strains of M. tuberculosis have slowly emerged, treatment failure is too often a fact. This infectious disease is the focus of renewed scientific interest (Janin, 2007).

Due to these facts, the alpha-chlorine-acetal obtained from the reaction of the phenazine of β-lapachone with triclorine-isocianuric acid (ATIC), named 14b-chloro-4a-methoxy-3,3-dimethyl-2,3,4a,14b-tetrahydro-1H-benzo[a]pyrano[2,3-c]phenazine, was assayed against Mycobacterium tuberculosis and showed Minimum Inhibitory Concentration (MIC) of 6.25 ng/ml in tests obtained for the evaluation of the tuberculostatic potencial, and established a new structural type with potential in future studies in medicinal chemistry. As the knowledge of its topology may assist in the understanding of its pharmacological behaviour, the crystal structure determination was undertaken in order to establish the perfect three-dimensional configuration of the molecule.

The bond lengths and angles in molecular structure of (I) are in accordance with values found in literature (Allen et al., 1987). The region of the molecule that contains the conjugated benzene ring attached to the phenazinic ring is planar, with the biggest distance to the plan of least squares, for the C14a [0.016 (1) Å]. The benzene ring plane (C4b—C8a) is inclined at an angle of 19.36 (5)° to this planar region of the conjugated rings. The piridinic ring presents a conformation of pure chair with puckering amplitude (Q) = 0.500 (2) Å, Θ = 13.9 (2)° and φ = 220.6 (9) ° (Cremer & Pople, 1975) while the ring formed by the atoms C4a—C4b—C8a—C8b—C14a and C14b has a conformation of half chair according to the puckering parameters: Q= 0.493 (2) Å, θ = 65.3 (2)° and φ= 335.6 (2)°. The two substituents, –Cl and –OMe are located in axial positions in the ring junction (Fig. 1). This special arrangement could be explained by anomeric effect toward the methoxy derivative.

In terms of biological activity, the lack of planarity would preclude its DNA intercalating activity, ruling out such type of DNA interaction. Alternative mechanisms of action should be searched to explain its significant tuberculostatic activity. Work on this line are in progress.