Crystal structures of sulfonamide protected bicyclic guanidines: (S)-8-{[(tert-butyl-dimethyl-sil-yl)-oxy]meth-yl}-1-[(2,2,4,6,7-penta-methyl-2,3-di-hydro-benzo-furan-5-yl)sulfon-yl]-1,3,4,6,7,8-hexa-hydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tri-fluoro-methane-sulfonate and (S)-8-(iodo-meth-yl)-1-tosyl-1,3,4,6,7,8-hexa-hydro-2H-pyrimido[1,2-a]pyrimidin-1-ium iodide.

Two compounds, (S)-8-{[(tert-butyl-dimethyl-sil-yl)-oxy]meth-yl}-1-[(2,2,4,6,7-penta-methyl-2,3-di-hydro-benzo-furan-5-yl)sulfon-yl]-1,3,4,6,7,8-hexa-hydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tri-fluoro-methane-sulfonate, C(27)H(46)N(3)O(4)SSi(+)·CF(3)O(3)S(-), (1) and (S)-8-(iodo-meth-yl)-1-tosyl-1,3,4,6,7,8-hexa-hydro-2H-pyrimido[1,2-a]pyrimidin-1-ium iodide, C(15)H(21)IN(3)O(2)S(+)·I(-), (2), have been synthesized and characterized. They are bicyclic guanidinium salts and were synthesized from N-(tert-but-oxy-carbon-yl)-l-me-thio-nine (Boc-l-Met-OH). The guanidine is protected by a 2,2,4,6,7-penta-methyl-dihydro-benzo-furan-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 intra-molecular hydrogen bond in a six-membered ring to the oxygen atom of the sulfonamide protecting group.