MAGNETIC RESONANCE IN CHEMISTRY Magn. Reson. Chem. 2002; 40: 477–479 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1024 Spectral Assignments and Reference Data 1 H and 13 C NMR spectral characterization of some antimalarial in vitro 2,4-diamino-10- methylpyrimido[4,5-b]-5-quinolone derivatives Jaime E. Charris, 1* Jos ´ e N. Dom´ ınguez, 1 Neira Gamboa, 2 Jorge Angel, 3 Nolberto Pi ˜ na, 3 Mayamar ´ u Guerra, 3 Elba Michelena 3 and Sim ´ on E. L ´ opez 4 1 Laboratorio de S´ ıntesis Org ´ anica, Universidad Central de Venezuela, Aptdo. 47206, Los Chaguaramos 1041-A, Caracas, Venezuela 2 Departamento de Biolog´ ıa, Facultad de Farmacia, Universidad Central de Venezuela, Caracas, Venezuela 3 Escuela de Qu´ ımica, Facultad Experimental de Ciencias, Universidad del Zulia, Maracaibo, Venezuela 4 Departamento de Qu´ ımica, Universidad Sim ´ on Bol´ ıvar, Caracas, Venezuela. Received 2 January 2002; accepted 28 January 2002 We report the 1 H NMR and 13 C NMR chemical shifts and J(H,H), J(H,F) and J(C,F) coupling constants of 13 2,4-diamino-10-methylpyrimido[4,5-b]-5-quinolone derivatives, some of them with moderate activity against Plasmodium falciparum in vitro. They were character- ized and assigned on the basis of 1 H, 13 C and 13 C– 1 H (short- and long-range) correlated spectra. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: NMR; 1 H NMR; 13 C NMR; quinolones; antimalarials INTRODUCTION Malaria is a major public health problem, endemic in over 100 countries in the world. The World Health Organization (WHO) estimates that there are 300 million clinical cases every year, with over 1 million deaths. 1 The emergence and spread of resistance to antimalarial drugs has highlighted the need for the discovery and development of novel antimalarial molecules. To achieve this goal, antimalarial drug research, on the one hand, needs to focus on validated targets in order to generate new drug candidates and, on the other hand, needs to identify the targets for the future by studying the basic metabolic and biochemical processes of the malaria parasite. 2,3 Also, we have recently reported the synthesis and spectral characterization of some 3-amino-9-phenylpyrazolo[3,4-b]-4-quinolones and 2,4-diamino-10- phenylpyrimido-[4,5-b]-5-quinolones. 4–7 These compounds proved to be an interesting family of antimalarial agents in vitro. In view of these findings, there has been renewed interest in our laboratories in the synthesis, identification and spectral characterization of new analogues bearing MeO, Cl and F substituents and a methyl group at position 10. In this paper we present 1 H NMR and 13 C NMR data for 2,4-diamino-10-methylpyrimido[4,5-b]-5-quinolone derivatives (Scheme 1). They have demonstrated a moderate antimalarial activity against a chloroquine-resistant strain of Plasmodium falciparum in vitro (IC 50 D ⊲1–3 ð 10 6 M) and no activity against in vitro non-enzymatic heme polymerization. L Correspondence to: Jaime E. Charris, Laboratorio de S ´ ıntesis Org ´ anica, Universidad Central de Venezuela, Aptdo. 47206, Los Chaguaramos 1041-A, Caracas, Venezuela. Contract/grant sponsor: IIF. Contract/grant sponsor: CDCH-UCV; Contract/grant number: PG 06-30-4590-2000. Contract/grant sponsor: CONICIT; Contract/grant number: LAB-97000665. Compound R R N O CH 3 N N N NH 2 H H 4 6 9 1-13 1 2 3 4 5 6 7 8 9 10 11 12 13 H 7-OMe 8-OMe 9-OMe 7,8-OMe 7,9-OMe 7-Me 8-Me 7-Cl 8-Cl 6,7-Cl 7,8-Cl 7-F 1 Scheme 1. Structures of 2,4-diamino-10-methylpyrimido[4,5-b]-5-qu- inolones 1 – 13. EXPERIMENTAL Compounds The quinolones 1–4 were synthesized according to the literature 6 and 5–13 were prepared by the synthetic route shown in Scheme 2. The respective phenyl isothiocyanate was condensed with ethyl cyanoacetate in potassium hydroxide, MeI and dry 1,4-dioxane, the resulting N,S-acetals I were cyclized thermally and finally the quinolones II were N-alkylated regiospecifically by heating with potassium carbonate, DMF and MeI. The final products III were obtained when II was reacted with guanidine sulfate and anhydrous potassium carbonate in DMF. The structures and purities of the compounds were confirmed by their melting-points, elemental analyses (Atlantic Microlab Inc., Norcross, GA, USA) and IR (Table 1) and NMR spectra. III II I N O CH 3 SCH 3 CN R R EtO 2 C N SMe CN H R N O CH 3 N N NH 2 NH 2 Scheme 2. Preparation of compounds 5 – 13. NMR spectroscopy NMR spectra were recorded on a JEOL EX 270 Fourier transform (FT) NMR spectrometer and Bruker AMX 500 FT (500 MHz) instrument using DMSO-d 6 ; tetramethylsilane was used as an internal standard. The instrument were equipped with a 5 mm broadband probe head. Processing was performed using the program DELTA V1.8, and XWIN NMR V2.5, respectively, running on a Silicon Graphics Workstation. In 1 H NMR experiments, the parameters were as follows: spectral window, 15 ppm; width of 30 ° pulse, 2 μs; relaxation delay, 4 s; and number of scans, 8. In the 13 C NMR experiments, the parameters were as follows: spectral window, 250 ppm; width of 30 ° pulse, 2.8 μs; relaxation delay, 2 s; and number of scans, 9000–10 000. 1 H, 13 C, COSY, HETCOR and FLOCK spectra were obtained using standard JEOL software. Heteronuclear 13 C– 1 H HETCOR experiments were carried out with a spectral width of 17 000 Hz for 13 C(F 2 ) and 4000 Hz for 1 H (F 1 ). The spectra were acquired with 1024 ð 128 data points. The data were processed by exponential multiplication (LB: 3Hz) in F 2 and sinusoidal multiplication in F 1 and zero filling was applied in F 1 . The mixing delay for single-bond correlation was 3.4 ms and for long-range bond correlation it was 70 ms and the relaxation delay was 1.5 s. Two-dimensional inverse hydrogen detected heteronuclear shift correlation HMQC spectra and long-range correlation HMBC were obtained with the standard Bruker pulse program [ 1 J(C,H): 140 Hz, F 2 27 930 Hz and F 1 5040 Hz, relaxation delay 1.5 s, 2K ð 128 data points. 2 J(C,H): 7 Hz, F 2 27 930 Hz and F 1 6666 Hz, relaxation delay 2.0 s, 2K ð 128 data points]. Copyright  2002 John Wiley & Sons, Ltd.