A method of synthesizing a heparin compound, comprising: providing a hexasaccharide comprising the following structure:, wherein R 2 is H or a detectable tag; elongating the hexasaccharide substrate to a heptasaccharide using heparosan synthase-2 and the substrate glucuronic acid (GlcUA); elongating the heptasaccharide substrate to an octasaccharide using N -acetyl glucosaminyl transferase and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the octasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized octasaccharide using 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); converting N-trifluoroacetyl glucosamine (GlcNTFA) residue(s) on the octasaccharide to N-sulfo glucosamine (GlcNS) residues using N-sulfotransferase, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), and a base to provide an octasaccharide substrate; elongating the octasaccharide substrate to a decasaccharide using heparosan synthase-2 and N -acetyl glucosaminyl transferase, and using substrates comprising glucuronic acid (GlcA) and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the decasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized decasaccharide using 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); converting N-trifluoroacetyl glucosamine (GlcNTFA) residue(s) on the resultant sulfated decasaccharide to N-sulfo glucosamine (GlcNS) residues using N-sulfotransferase, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), and a base to provide a decasaccharide substrate; elongating the decasaccharide substrate to a dodecasaccharide using heparosan synthase-2 and N -acetyl glucosaminyl transferase, and using substrates comprising glucuronic acid (GlcA) and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the dodecasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized dodecasaccharide using (i) 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); (ii) 6-O-sulfotransferase (6-OST), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); and (iii) 3-O-sulfotransferase 1 (3-OST-1), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); wherein a heparin compound represented by the following structure is synthesized: providing a hexasaccharide comprising the following structure:, wherein R 2 is H or a detectable tag; elongating the hexasaccharide substrate to a heptasaccharide using heparosan synthase-2 and the substrate glucuronic acid (GlcUA); elongating the heptasaccharide substrate to an octasaccharide using N -acetyl glucosaminyl transferase and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the octasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized octasaccharide using 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); converting N-trifluoroacetyl glucosamine (GlcNTFA) residue(s) on the octasaccharide to N-sulfo glucosamine (GlcNS) residues using N-sulfotransferase, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), and a base to provide an octasaccharide substrate; elongating the octasaccharide substrate to a decasaccharide using heparosan synthase-2 and N -acetyl glucosaminyl transferase, and using substrates comprising glucuronic acid (GlcA) and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the decasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized decasaccharide using 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); converting N-trifluoroacetyl glucosamine (GlcNTFA) residue(s) on the resultant sulfated decasaccharide to N-sulfo glucosamine (GlcNS) residues using N-sulfotransferase, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), and a base to provide a decasaccharide substrate; elongating the decasaccharide substrate to a dodecasaccharide using heparosan synthase-2 and N -acetyl glucosaminyl transferase, and using substrates comprising glucuronic acid (GlcA) and N-trifluoroacetyl glucosamine (GlcNTFA); epimerizing the dodecasaccharide using C 5 -epimerase (C 5 -epi); sulfating the resultant epimerized dodecasaccharide using (i) 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); (ii) 6-O-sulfotransferase (6-OST), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); and (iii) 3-O-sulfotransferase 1 (3-OST-1), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); (i) 2-O-sulfotransferase (2-OST) and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); (ii) 6-O-sulfotransferase (6-OST), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); and (iii) 3-O-sulfotransferase 1 (3-OST-1), and 3'-phosphoadenosine 5'-phosphosulfate (PAPS); wherein a heparin compound represented by the following structure is synthesized: