in the early 1960s, woodward began work on what was the most complex natural product synthesized to date- vitamin b12. in a remarkable collaboration with his colleague albert eschenmoser in zurich, a team of almost one hundred students and postdoctoral workers worked for many years on the synthesis of this molecule. the work was finally published in 1973, and it marked a landmark in the history of organic chemistry. the synthesis included almost a hundred steps, and involved the rigorous planning and analyses that had always characterised woodward's work. this work, more than any other, convinced organic chemists that the synthesis of any complex substance was possible, given enough time and planning. however, as of 2006, no other total synthesis of vitamin b12 has been published.