Synthesis and Crystal Structure of N-[(2S)-4-bromo-2-(L-menthyloxy)-5-oxo-2,5-dihydro-3-furyl]-L-leucine

Starting from (5S)-(L-menthyloxy)-3,4-dibromo-5H-furan-2-one and L-leucine, the title compound N-[(2S)-4-bromo-2-(L-menthyloxy)-5-oxo-2,5-dihydro-3-furyl]-L-leucine 5 (C(20)H(32)BrNO(5), M(r) = 446.37) was obtained in one-pot process via the tandem Michael addition-elimination reaction in the presence of potassium hydroxide. The chemical structure and absolute configuration of the title compound were confirmed via rotation, UV-Vis, FT-IR, (1)H NMR, (13)C NMR, MS and elemental analysis, especially by the X-ray single-crystal diffraction. The crystal crystallizes in an orthorhombic system, space group P2(1)2(1)2(1) with a = 12.5249(16), b = 19.005(3), c = 19.719(3) angstrom, V = 4693.7(10) angstrom(3), Z = 8, D(c) = 1.263 g/m(3), mu = 1.778 mm(-1), F(000) = 1872, the final R = 0.0617 and wR = 0.1576 for 3967 observed reflections (I > 2 sigma(I)). X-ray analysis reveals that the title compound has two independent molecules in the asymmetric part of the unit cell with the two five-membered furanones being almost planar. The essential part of the electron delocalization is concentrated in the N(1), C(3), C(1), C(37) and O(7) region and N(2), C(28), C(27), C(30) and O(4) region in the other molecule respectively, but does not take place at the expense of delocalization within the ester function.