Cytel Receives Carbohydrate Process Patent
Cytel Corporation has been awarded U.S. Patent 5,728,554 ("Improved enzymatic synthesis of glycosidic linkages") for an improved carbohydrate synthesis method based on the firm's Sugar Nucleotide Cycling (SNC) technology. The patent covers a novel method of controlling enzymatic reactions, resulting in yields of specialized carbohydrates approaching 100%.
"Traditionally, it has been very difficult to work with carbohydrates due to the high cost associated with producing these complex compounds," said Virgil Thompson, Cytel's President and Chief Executive Officer. "With this exclusive technology, Cytel can provide these specialized molecules more cost effectively."
The patent covers the enzymatic synthesis of oligosaccharides (complex carbohydrates) using specialized recombinant glycosyltransferases, enzymes that form the appropriate chemical linkages necessary in creating tailor-made carbohydrate products.
Sugar Nucleotide Cycling(TM) technology is used to assemble complex and specific bioactive carbohydrates on a commercial scale, as well as for synthetic remodeling of carbohydrates or recombinant glycoproteins. The technology imitates the natural carbohydrate synthesis process requiring a cascade of chemical reactions initiated by specialized enzymes. The method is more time- and cost- effective than conventional chemical synthesis technologies, especially solid-phase synthesis, a time-consuming process with limited throughput.
The Technology
Of all the major classes of organic molecules, carbohydrates are the least-represented in the pharmaceutical world. The reason is simple: carbohydrates are difficult to work with. The molecules are extremely hydrophilic, so most convenient organic solvents are not usable; moreover reaction specificity (carbohydrates have multiple hydroxyl groups) is problematic unless protecting groups are used extensively. Carbohydrate synthesis on a large scale is possible, but difficult.
Cytel's SNC process uses enzymes, instead of chemical reagents, to form chemical bonds between sugar units. Enzymatic reactions require no protecting groups, are regioselective (i.e. they select one hydroxyl group over others), stereoselective (react with only the right optical isomer), and operate in water.
SNC requires the glycosyl transferase enzyme, a donor substrate, an acceptor sugar, and a divalent metal cation (Mn2+, Mg2+, Cu2+, Co2+, Zn2+, or combinations of these ions). The addition of each sugar building block occurs at the non-reducing end of the oligosaccharide substrate. Actually the substrate may be a sugar, glycoprotein, glycolipid, phospholipid, sphingolipid, or a ganglioside, which broadens the range of potential therapeutic molecules that may be built up using SNC.
Figure 1 illustrates the SCN process. The sugar unit being added (S) to the growing carbohydrate acceptor molecule (C) is first conjugated enzymatically with a nucleotide base (N). A second enzyme, the sugar transferase, then transfers the sugar unit to the carbohydrate acceptor. The process is repeated as many times as necessary to build up a carbohydrate of the required length and composition. What is not indicated in the figure is the importance of the metal species. The patent indicates that as sugar solution is added to the reaction, the concentration of metal ion must be maintained in the 50 mM range to ensure enzyme activity.
By Angelo DePalma
For more information: Virgil Thompson, President and CEO, Cytel Corp., 3525 John Hopkins Ct., San Diego, CA 92121. Tel: 619-552-3000.