Acenaphthenequinone (0.182 g, 1 mmol), ethyl-4-aminobenzoate (0.165 g, 1 mmol) and 30.0 mL of methanol were placed in 100 mL round bottom flask. The mixture was allowed to heat under reflux for overnight in the presence of formic acid. The solvent was removed to give the crude compound. Single crystal suitable for Xray crystallography was obtained after recrystallization from ethanol. Yield: 73%. m.p.: 211˚C - 212˚C. Anal. Calcd for C₂₁H₁₅NO₃: C 76.60, H 4.56, N 4.26%; found: C 76.94, H 4.33, N 4.38%. Main IR bands (KBr, cm⁻¹): 2983 (w), 1729 (m), 1702 (s), 1666 (m), 1600 (s), 1275 (s), 1237 (m), 1107 (m), 1014 (m), 781 (m). ¹H-NMR 500 MHz, (DMSO-d₆, ppm): δ 1.37 (3H, t, CH₃), 4.36 (2H, q, CH₂), 6.79 (1H, d, H8), 7.22 (2H, d, H14), 7.59 (1H, t, H7), 7.93 (1H, t, H3), 8.11 (2H, d, H15), 8.16 (1H, d, H2), 8.22 (1H, d, H6), 8.39 (1H, d, H4). ¹³C-NMR (ppm): δ 14.21, 60.67, 117.77, 121.94, 123.19, 126.19, 126.39, 128.45, 128.62, 129.83, 130.15, 130.66, 130.90, 132.41, 142.68, 154. 98, 158.96 (C=N), 165.39 (C=O), 188.32 (C=O).

Crystal data was collected using Bruker APEXII DUO area-detector diffractometer with graphite monochromated MoKα radiation at a detector distance of 50 mm and collected under 100 K using Oxford Cryosystem Cobra low temperature attachement [12]. The cell refinement and data reduction were performed using SAINT program [13] and the empirical absorption correction was performed using the SADABS program [13]. The structure was solved by direct methods and refined by leastsquares using SHLEXTL software package [14]. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in idealized position, and refined using a riding model. The details of the crystal data and structure refinements are given in Table 1.

E4AB was tested for the antibacterial activity against B. subtilis and Enterobacter by slight modification of the disc-diffusion method described by Murray et al. [15]. 0.1 mL of 10⁸ CFU/mL of bacteria suspension was streaked evenly onto the agar containing Petri plate. The plate was then allowed to air dry in laminar flow. E4AB was dissolved in DMSO to get 1000, 500 and 250 µg/mL concentrations of the compound. Four sterilized filter paper discs (diameter 7 mm) were placed at four equidistant places on the inoculated plate. 20 µL of each concentration of the compound was spiked on the disc accordingly by using micropipette. Filter paper disc treated with DMSO was served as the control in the test. Lastly, the inoculated plate was allowed to air dry and incubated under room temperature (25˚C ± 2˚C) for 48 hours before the inhibition zone was recorded in diameter (mm). Each test was conducted in triplicate. In the

Table 1. Crystal data, data collection and refinement parameters of E4AB.

antifungal activity against Foc the same method as described for antibacterial activity was applied except for the amount of fungal suspension and incubation period used which were 1 mL of 1 × 10⁴ spore/mL suspension and seven days, respectively.

In E4AB (Figure 1), the acenaphthylenone moiety is essentially planar, with atom C10 deviates from the mean plane formed by a maximum deviation of −0.057(1) Å. Nevertheless, the whole molecule is not planar, as indicated by the dihedral angle between the mean planes through the acenaphthylenone moiety and phenyl ring being 74.44(3)˚. The ethyl formate group is slightly inclined at a dihedral angle of 12.01(5)˚ with respect to the attached phenyl ring. In the crystal packing (Figure 2), adjacent molecules are interconnected into one-dimensional hydrogen-bonded chains propagating along the a axis via intermolecular C-HO hydrogen bonds

[CO distance of 3.4010(11) Å]. Further stabilization of the crystal packing is provided by weak intermolecular ππ aromatic stacking interactions [centroid-centroid distance of 3.7102(6) Å] involving the C5-C10 phenyl ring. The selected bond lengths and bond angles are given in Table 2.

E4AB displays two stretching bands at 1729 and 1702 cm⁻¹ which are corresponded to the C=O stretching vi

Table 2. Selected bond angles (˚) and bond lengths (Å) of E4AB.

brations of the ester and the ketone, respectively [16]. Meanwhile the ν (C=N) band is assigned to an absorption at 1666 cm⁻¹ [17]. The characteristic aromatic ring C=C stretching frequency is observed at 1600 cm⁻¹ [2]. In the IR spectrum of E4AB, the C-H stretch of sp³ hybrid carbon atom appears at 2983 cm⁻¹.

¹H-NMR spectrum of E4AB is shown in Figure 3. A triplet at δ 1.37 ppm and a quartet at δ 4.36 ppm are assigned to H19 and H18, respectively. H8 which is ortho magnetically coupled to H7 appears as a doublet at δ 6.79 ppm with a coupling constant of 7.5 Hz. Meanwhile the doublet at δ 7.22 ppm is attributed to H14 which is coupled to H15 (δ 8.11 ppm). H7 and H3 are observed as triplets at δ 7.59 and 7.93 ppm, respectively. H7 is coupled to H8 and H6 while H3 is coupled to H2 and H4

where H2, H4 and H6 are assigned to doublets at δ 8.16, 8.39 and 8.22 ppm, respectively. The assignment of naphthalene protons to the corresponding signals are in agreement with the previously reported observations by Wang et al. [18] and Yang et al. [19].

The antimicrobial activity of the title compound in DMSO solution was assayed against two bacteria and one fungus by disc-diffusion method employing 1000, 500 and 250 µg/mL concentrations of the compound. The effectiveness of an antimicrobial agent in sensitivity testing is based on the size of zone of inhibition. The diameter of the zone is measured to the nearest millimeter. The result (Table 3) shows that at higher concentration, the Gram-negative bacterium (Enterobacter) is more sensitive towards E4AB than the Gram-positive bacterium (B. subtilis). E4AB also exhibits relatively potent inhibitory activity against Foc.