The sugar-modified Schiff base ligand benzyl 2-deoxy-2-salicylideneamino-alpha-D-glucopyranoside H2L, prepared by condensation of salicylaldehyde and the monomeric chitosan analogue benzyl 2-deoxy-2-amino-alpha-D-glucopyranoside, reacts with copper(II) acetate to form a self-assembled, alkoxo-bridged tetranuclear homoleptic copper(II) complex [{Cu(L)141 (4) with Cu4O4 heterocubane core. The chiral complex 4 crystallizes in the space group P2(1)2(1)2(1). The tetranuclear complex 4 is composed of two dinuclear Cu(L)12 entities linked by the four M-bridging C-3 alkoxide oxygen atoms of the sugar backbone. The preorganization of the dimeric (Cu(L)12 entities is enforced by strong hydrogen bonds between the phenolate oxygen atom and the C-4 hydroxy group of the two constituting chiral monomeric building blocks. Therefore the Cu4O4 core can be classified as a type I or 2 + 4 cubane. The chirality of the structure is confirmed by circular dichroism (CD) spectra, which reveal a significant dichroism associated with the copper centered transitions at around 600 nm. Temperature dependent magnetic susceptibility measurements indicate ferromagnetic exchange interactions in complex 4. Fitting of the experimental data with a two J model based on the 2 + 4 topology ((H) over cap = -J(1)((S) over cap (1)(S) over cap (3) + (S) over cap (2)(S) over cap (4)) - J(2)((S) over cap (1) + (S) over cap (3))((S) over cap (2) + (S) over cap (4))) leads to exchange coupling constants of J, = 64 and J2 = 4 cm(-1). The observed ferromagnetic coupling can be attributed to the very small Cu-O-Cu bridging angles within the Cu2O2 core of the constituting dimeric entities, which are a result of the conformational requirements introduced by the sugar backbone. 4 is not only the first example of an alkoxo-bridged tetranuclear copper(II) complex with Cu4O4 core representing the 2 + 4 cubane class with ferromagnetic ground state but also a rare example for the class of molecules combining a ferromagnetic ground state with optical activity. The ferromagnetic S = 2 ground state of 4 is confirmed by magnetization measurements and ESR spectroscopy.