Three new capped porphyrins, H-2(OC(2)OPor) (7), H-2(OC(CO)NPor) (13),
and H-2(OC(2)NPor) (14), to be used as heme model compounds, have bee
n synthesized and characterized. These compounds have the shortest lin
kages between cap and porphyrin plane of any four-arm capped porphyrin
s synthesized to date. The general synthetic procedure for H-2(OC(2)OP
or) involves the reaction of a tetraaldehyde ''cap'' with pyrrole to f
orm the capped porphyrin. In the synthesis of the tetraamide-capped po
rphyrin, H-2(OC(CO)NPor), a tetraacid chloride cap is reacted with ,al
pha,alpha,alpha-tetra-(o-aminophenyl)porphyrin. The amide groups may b
e reduced to form H-2(OC(2)NPor). With the use of FeBr2, Fe2+ may be i
nserted in high yield into Ha(2)(OC(2)OPor) and H-2(OC(CO)NPor). The c
rystal structures of H-2(OC(2)NPor), Fe(OC(2)OPor)(OMe), and [Fe(OC(2)
OPor)](2)(mu-O) provide details on the types and amounts of cap expans
ion necessary to accommodate small ligands of biological interest, suc
h as O-2 and CO.