Table 3.

Comparison of three strategies for complex glycan production

	Chemical synthesis	Enzymatic synthesis	Reverse synthesis
Starting material	Monosaccharides	Monosaccharides,Sugar nucleotides	Glycoconjugates
Protecting group	Multiple protecting groups	Not needed	Single protecting group(tag) at reducing end
Reagents	Solvents, activator, catalysts, etc.	multiple enzymes, buffers	Bleach, tag installation and removal
Operation	Various reaction conditions, special expertise required	Easy	Easy
Scale	milligram to gram	milligram to gram	milligram to gram
Purification	Relatively simple	Relatively simple	Multi-dimensional HPLC
Library synthesis	Mostly linear	Could be parallel	Parallel
biomedical relevance of products	Un-certain	Likely	Nearly certain
Major advantage	Chemical versatility	Easy operation	Product diversity and biological relevance
Major bottle neck	High technical threshhold, labor intensive	Enzyme availability, reagents cost	Intensive purification and structural identification
Automation perspective	Developing	Developing	High potential