452
Antitumor Steroids
HO
OH
7
Re
S
N
S
S
C
N
4
S
3
S
Re
CO
Br
OC
CO
G
4
X
=
O
X
=
NH
O
4
X
=
NH
G
3
O
X
=
NH
G
X
O
G
=
HO
OH
C
C
H
11
11
b
-EE
2
C
C
H
Co
2
(CO)
6
C
C
Re(CO)
3
Re(CO
3
)
Fig. 7
Organometallic E
2
derivatives – chemical formulas of 7
α
and 11
β
derivatives described
in Sect. 4.1.2.
promotes
an
interaction
with
a
vic-
inal
nucleophilic
residue.
Among
E
2
transition-metal complexes examined, di-
cobalt
clusters
[Co
2
(CO)
6
]w
e
r
ef
o
u
n
d
to
be
the
most
active
afFnity
mark-
ers. Of note, ±eCo-(CO)
6
(17
α
-ethynyl-17
β
-
dehydroxyestradiol) in which the heter-
obimetallic fragment is sterically simi-
lar to the Co
2
(CO)
6
homolog, prevents
the formation of
a carbenium-ion-like
species conFrming the requirement at
the 17-position of an OH group and an
organometallic unit capable of dissipating
the positive charge of the transient carbo-
cation.
Potential influence of covalent binding
of these dicobalt clusters on the ER level
and transcriptional activity is unknown,
and therefore, to be investigated. Poten-
tial therapeutic activity should also be
assessed. Note in this regard that alkyne
Co
2
(CO)
6
itself shows no cytotoxic effect.
