Natural hexosaminoglycan heparin remains the most commonly prescribed anticoagulant in hospitalized patients. However its administration could induce side clinical events, including thrombocytopenia and bleeding. This explaines the need of development of alternative anticoagulant drugs based on modified heparin and polyanionic oligo- and polysaccharide derivatives, such as sulfated glucans, phosphomannans and fucoidans. Here we review the works on the synthesis of oligosaccharides related to low molecular weight hepain fragments and their derivatives, as well as oligosaccharides, which imitate parts of heparin chain responsible for biological activity. These works were aimed to develop the pharmaceutical preparations lacking ofheparin disadvantages.