5-Methyl-3,6,7,8a-tetrahydro-2H-diimidazo[1,2-c:1′,2′-e]pyrido[1,2-a][1,3,5]triazin-5-ium iodide

The structure of the title compound, C12H16N5 +·I−, shows that the methylation reaction with CH3I occurred at the imine N atom at position 5 of the 3,6,7,8a-tetrahydro-2H-diimidazo[1,2-c:1′,2′-e]pyrido[1,2-a][1,3,5]triazine system. In the cation, the sp 3-hybridized C atom belonging to the fused dihydropyrine and dihydro-1,3,5-triazine rings deviates by 0.514 (3) Å from the best plane defined by the remaining cationic non-H atoms. The fused dihydropyridine and dihydro-1,3,5-triazine rings are each in a half-chair conformation with the sp 3-hybridized C atom as a flap. The iodide anion is 3.573 (2) Å from the methylated N atom and exhibits five short C—H⋯I− contacts with distances less than 3.16 Å. The structure has been determined from a non-merohedral twin with twin law [−1 0 0 0 − 1 0 0.115 0 1], minor domain = 0.1559 (12).

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2676).

Comment
Biguanide derivatives are known to possess diverse biological activities, including antidiabetic, antibacterial, germicidic, antiviral and antimalarial. On the other hand, quaternary ammonium salts constitute a well known class of bacteriostatic agents. Therefore, we have decided to synthesize some N-alkylated cyclic biguanide derivatives for biological testing, based on the previously described procedure (Sączewski & Foks, 1981) which consists in the reaction of 2,3,6,7,8a,13-hexahydropyrido[1,2-a]diimidazo[1',2'-c:1'',2''-e]-1,3,5-triazine (1) with an alkyl halide. As shown in Fig. 1, the course of the reaction of 1 with methyl iodide has not been established and two products, 2 or 3, arising from either N1 or N5 alkylation have been proposed. In this work, based on X-ray structure analysis ( Fig. 2) and hetero-correlation NMR experiments (HSQC and HMBC), the structure of the title compound (2) is determined unambiguously. Regioselectivity of N-alkylation of the cyclic biguanide derivative 1 could not be predicted on the basis of calculated electrostatic potential and charge distribution.
The structure of the N5 alkylated product 2 was also confirmed by 2D NMR spectroscopic data. Thus, assignment of signals observed in 1 H and 13 C-NMR spectra was possible using HSQC spectrum (see numbering scheme in Fig. 3). The crucial signals of quaternary carbon atoms C13a and C4a were found at 145.7 and 152.6 p.p.m., respectively. 3-Bond correlation from the latter carbon to a singlet of three protons at 3.26 p.p.m. observed in the HMBC spectrum (Fig. 4) indicated the placement of methyl group at the N5 nitrogen atom.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.