4-((S)-2-tert-Butoxycarbonyl-2-tert-butoxycarbonylamino-ethyl)-1-((2S,5S)-5-tert-butoxycarbonyl-5-tert-butoxycarbonylamino-2-hydroxy-pentyl)-3-((S)-3-tert-butoxycarbonyl-3-tert-butoxycarbonylamino-propyl)-5-hydroxy-pyridinium