Synthesis of novel pendant arm macrocyclic ligands as potential models for enterobactin
Date
2018-07-09
Authors
Cameron, Beth
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Abstract
A series of pendant arm tris-catecholate macrocyclic
ligands were synthesized. The first, based on 1,4,7-
triaminopropyl-1, 4, 7-triazacyclononane, was prepared via
condensation with 2,3-dimethoxybenzoyl chloride. The
deprotection of the catechol moieties was achieved with boron
tribromide in 80% yields. The ferric complexes were
characterized by electronic absorption spectroscopy.
The second series of ligands described are based on the
pendant arm macrocyclic ligand, 1, 4, 7-triaminoethyl-1, 4, 7-
triazacyclononane. New routes to the preparation of this
ligand were investigated; the best approach used chloroacetyl
chloride as the reagent in functionalizing the nitrogen atoms
of the triazacyclononane ring. The ligands, 1, 4, 7-tris-((2, 3-
dihydroxyphenethyl) aminoethyl)-1, 4, 7-triazacyclononane (34)
and 1, 4, 7-tris-((2, 3-dihydroxybenzyl)aminoethyl)-1, 4, 7-
triazacyclononane (36) were prepared through a series of acid
chloride condensation reactions, followed by reduction of the
amides with diborane.
The mononuclear ferric complexes of compounds 34 and 36
Were prepared and characterized by uv-visible spectroscopy.
Mononuclear nickel, cobalt, and copper complexes of these
ligands were also characterized by uv-visible spectroscopy.
The binuclear complexes, Na[NiFe(34)] and Na[NiFe(36)], were prepared and characterized by electronic absorption
spectroscopy.
Tris-((2, 3-dihydroxybenzylamino)ethyl) amine, tris-((2, 3-
dihydroxybenzoyl)aminoethyl)amine, and
tris-((2 ,3-dihydroxyphenethyl)aminoethyl)amine were prepared
by Schiff base condensation reactions, or acid chloride
condensation of tris-(2-aminoethyl)amine and the appropriate
catecholate moiety. The ferric complexes of these ligands
were prepared and characterized by uv-visible spectroscopy.
The A1(III) tris-((2,3-dihydroxybenzyl)aminoethyl)amine
complex was examined by nmr spectroscopy. The Ni(II), Cu(Il)
and Co(III) complexes were investigated by electronic
absorption spectroscopy.
The rates of base hydrolysis of [Co(tacn) (en)Cl]2+
(tacn=1, 4, 7-triazacyclononane), [Co(tacn) (amp)Cl]2+ (amp=2-
aminomethylpyridine), [Co(tacn) (tn)Cl]2+, ufac-I-
[Co(dien) (amp)Cl]2+ (dien=l,4,7-triazaheptane), ufac-Il-
[Co (dien) (amp)]2+ and [Co (bicycloN5) C1]2+
(bicycloN5=1, 5, 8, 12, 15-pentaazabicyclo [10.5.2] nonadecane),
were measured using stopped flow techniques. The base
hydrolysis rates (kCH, M-1s-1; [ionic strength (M)]) are 9.66
[0.1], 154 [0.1], 40.6 [0.1], 334 [0.1], 762 [0.1], and 3X103
[1.0], respectively.
The rate of [NCS-] anation of [Co (bicycloN5) (OH2)]3+, and
the rates of [Br-] and [NCS-] anation of [Co (tacn) (en) (OH2)]3+
were measured as a function of pH. The pKa of the coordinated
water molecules are 3.8 ([Co (bicycloN5) (OH2)]3+) and 6.5
((Co(tacn) (en) (OH2)]3+) . The anation rates increase as the pH
increases, indicating a base catalysed anation reaction
through the deprotonation of the coordinated amine. In the
case of the [Co(tacn) (en) (OH2)]3+ complex, the rate increases
as the pH increases until the pH ~ 7, then there is no
reaction after that point, suggesting some sort of blockage at
the five-coordinate intermediate.
Description
Keywords
Macrocyclic compounds, Ligands