Crystal structures of sulfonamide protected bicyclic guanidines: (S)-8-{[(ferf-butyldimethylsilyl)oxy]-methyl}-1-[(2,2,4,6,7-pentamethyl-2,3-dihydro-benzofuran-5-yl)sulfonyl]-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-ium trifluoro-methanesulfonate and (S)-8-(iodomethyl)-1-tosyl-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidin-1-ium iodide.

Two compounds, (S)-8-{[(tert-butyldimethylsilyl)oxy]methyl|-1-[(2,2,4,6,7-pentamethyl-2,3-dihydrobenzofuran-5-yl)sulfonyl]-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-α]pyrimidin-1-ium trifluoromethanesulfonate, C27H46N3O4SSi+⋅-CF3O3S-, (1) and (S)-8-(iodomethyl)-1-tosyl-1,3,4,6,7,8-hexahydro-2#-pyri-mido[1,2-α]pyrimidin-1-ium iodide, C15H21IN3O2S⋅+I-, (2), have been synthesized and characterized. They are bicyclic guanidinium salts and were synthesized from N-(tert-butoxycarbonyl)-L-methionine (Boc-L-Met-OH). The guanidine is protected by a 2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl (Pbf, 1) or a tosyl (2) group. In the crystals of both compounds, the guanidinium group is almost planar and the N-H forms an intramolecular hydrogen bond in a six-membered ring to the oxygen atom of the sulfonamide protecting group. [ABSTRACT FROM AUTHOR]