An enantiospecific synthesis of the tricyclic guanidine segment 19 of the new anti-HIV alkaloid batzelladine A, isolated from a marine sponge of gen us batzella, starting from [3R(1'R,4R)]-4-acetoxy-3-[1-(tert-butyldimethylsilyloxy)ethyl]-2-azetidinone 3 is described.