To substantiate the chemical structure of MyxA, we have developed a total synthesis program for both proposed structures. Our retrosynthesis gave four major fragments A-D. This and the forward syntheses exemplified for the revised structure of MyxA are shown in Fig. (for details, see SI). Extensive optimizations (solid-phase synthesis vs. solution-phase synthesis) revealed that fragment A should preferably be prepared by microwave-accelerated solid-phase synthesis, since we observed epimerizations during its preparation in the solution phase. In contrast, fragments B-D can be prepared in large scale in solution, and the same is true for the final peptide coupling reactions and deprotection steps.