CORM-EDE1: A Highly Water-Soluble and Nontoxic Manganese-Based photoCORM with a Biogenic Ligand Sphere

[Mn­(CO)5Br] reacts with
cysteamine and 4-amino-thiophenyl with a ratio of 2:3 in refluxing
tetrahydrofuran to the complexes of the type [{(OC)3Mn}2­(μ-SCH2CH2NH3)3]­Br2 (1, CORM-EDE1) and [{(OC)3­Mn}2(μ-SC6H4-4-NH3)3]­Br2 (2, CORM-EDE2).
Compound 2 precipitates during refluxing of the tetrahydrofuran
solution as a yellow solid whereas 1 forms a red oil
that slowly solidifies. Recrystallization of 2 from water
yields the HBr-free complex [{(OC)3Mn}2(μ-S-C6H4-4-NH2)2­(μ-SC6H4-4-NH3)] (3). The n-propylthiolate ligand (which is isoelectronic to the bridging
thiolate of 1) leads to the formation of the di- and
tetranuclear complexes [(OC)4Mn­(μ-S-nPr)2]2 and [(OC)3Mn­(μ-S-nPr)]4. CORM-EDE1 possesses ideal properties
to administer carbon monoxide to biological and medicinal tissues
upon irradiation (photoCORM). Isolated crystalline CORM-EDE1 can be
handled at ambient and aerobic conditions. This complex is nontoxic,
highly soluble in water, and indefinitely stable therein in the absence
of air and phosphate buffer. CORM-EDE1 is stable as frozen stock in
aqueous solution without any limitations, and these stock solutions
maintain their CO release properties. The reducing dithionite does
not interact with CORM-EDE1, and therefore, the myoglobin assay represents
a valuable tool to study the release kinetics of this photoCORM. After
CO liberation, the formation of MnHPO4 in aqueous buffer
solution can be verified.