Complexes of Furonewguinone B with a Cu 2+ Ion. A DFT Study
179
and O atoms present, HPJA has the three phenol OHs and the keto O14 typical of
ACPLs (as shown in Fig. 1) and an additional OH in R
; ARZ has the three phenol
OHs and O14 as in Fig. 1, an additional OH and an additional keto O attached to the
pyranoid ring, and the O heteroatom in the pyranoid ring; HPGB has only O14 and
O8–H15 corresponding to Fig. 1, because O10 is incorporated in the fused pyranoid
ring and O12 is a keto O; FNGB has O8–H15, O10–H16 and O14 corresponding to
Fig. 1, an additional OH at C3 and an additional OH attached to the furanoid ring,
and O12 is a keto O. In terms of C=C π bonds (besides the π system of the benzene
ring), HPJA has a π bond in R
(π1); ARZ has a π bond in the prenyl chain at C5
(π1) and two π bonds in the pyranoid ring (π2 and π3); HPGB has a π bond in the
prenyl chain at C5 (π1) and another in the pyranoid ring (π2); and FNGB has one
in the prenyl chain at C5 (π1). The structures of HPJA, ARZ and HPGB are shown
after the table of values in table S20.
It is interesting to compare relevant features for the complexes of these molecules
with a Cu
2+ ion. A thorough comparison of the effects of complexation on IHBs
has been carried out in a separate work [59], because of the importance of IHBs
for biologically active molecules and for analysing conformational preferences in
general. Table S20 attempts a comparison of other relevant features. The terms of
the comparison are not straightforward because the different structural features of
the molecules entail different binding possibilities and binding site preferences for
the ion and, consequently, a variety of other differences. It was opted to consider
partially-qualitative criteria for the comparison, and to include also those applicable
to types of complexes possible for all these molecules, such as the characteristics of
complexes in which the ion binds to O14 or to O12.
The number of calculated complexes is different for the different molecules,
because it depends on the variety of conformers and of possible binding sites. In
all cases, the calculated complexes comprise not only the lowest energy ones, but a
number of high energy (totally unpopulated) ones; the latter cannot be related to the
behaviour or to the biological activity of the complex, but are interesting to investigate the effects of specific changes (changes in the binding site, in the conformer
geometry, and the like).
The most preferred binding option for HPJA, ARZ and HPGB is simultaneous
binding to an O atom and a π bond; the second and third preferred binding options
entail either simultaneous binding to another O atom and a π bond or simultaneous
binding to two O atoms. For FNGB, the three preferred binding sites involve simultaneous binding to two or three O atoms; the phenomenon described at the end of
Sect. 3.3. suggests that the presence of O30–H31 somehow makes binding to π1
unfavourable. The lowest energy complex in which the ion binds to O14 has high
relative energy for all these molecules, with comparable values for HPJA, ARZ and
HPGB (≈15 kcal/mol) and higher value for FNGB.
HPJA has the best MIA values, followed by ARZ, which is closely followed by
HPGB, while FNGB has the poorest MIA. The trend is highlighted by the comparison of the MIA ranges, and also by the comparison of the MIA of corresponding
complexes. The comparison of the complexes with Cu binding to O14 is the most
179
and O atoms present, HPJA has the three phenol OHs and the keto O14 typical of
ACPLs (as shown in Fig. 1) and an additional OH in R
; ARZ has the three phenol
OHs and O14 as in Fig. 1, an additional OH and an additional keto O attached to the
pyranoid ring, and the O heteroatom in the pyranoid ring; HPGB has only O14 and
O8–H15 corresponding to Fig. 1, because O10 is incorporated in the fused pyranoid
ring and O12 is a keto O; FNGB has O8–H15, O10–H16 and O14 corresponding to
Fig. 1, an additional OH at C3 and an additional OH attached to the furanoid ring,
and O12 is a keto O. In terms of C=C π bonds (besides the π system of the benzene
ring), HPJA has a π bond in R
(π1); ARZ has a π bond in the prenyl chain at C5
(π1) and two π bonds in the pyranoid ring (π2 and π3); HPGB has a π bond in the
prenyl chain at C5 (π1) and another in the pyranoid ring (π2); and FNGB has one
in the prenyl chain at C5 (π1). The structures of HPJA, ARZ and HPGB are shown
after the table of values in table S20.
It is interesting to compare relevant features for the complexes of these molecules
with a Cu
2+ ion. A thorough comparison of the effects of complexation on IHBs
has been carried out in a separate work [59], because of the importance of IHBs
for biologically active molecules and for analysing conformational preferences in
general. Table S20 attempts a comparison of other relevant features. The terms of
the comparison are not straightforward because the different structural features of
the molecules entail different binding possibilities and binding site preferences for
the ion and, consequently, a variety of other differences. It was opted to consider
partially-qualitative criteria for the comparison, and to include also those applicable
to types of complexes possible for all these molecules, such as the characteristics of
complexes in which the ion binds to O14 or to O12.
The number of calculated complexes is different for the different molecules,
because it depends on the variety of conformers and of possible binding sites. In
all cases, the calculated complexes comprise not only the lowest energy ones, but a
number of high energy (totally unpopulated) ones; the latter cannot be related to the
behaviour or to the biological activity of the complex, but are interesting to investigate the effects of specific changes (changes in the binding site, in the conformer
geometry, and the like).
The most preferred binding option for HPJA, ARZ and HPGB is simultaneous
binding to an O atom and a π bond; the second and third preferred binding options
entail either simultaneous binding to another O atom and a π bond or simultaneous
binding to two O atoms. For FNGB, the three preferred binding sites involve simultaneous binding to two or three O atoms; the phenomenon described at the end of
Sect. 3.3. suggests that the presence of O30–H31 somehow makes binding to π1
unfavourable. The lowest energy complex in which the ion binds to O14 has high
relative energy for all these molecules, with comparable values for HPJA, ARZ and
HPGB (≈15 kcal/mol) and higher value for FNGB.
HPJA has the best MIA values, followed by ARZ, which is closely followed by
HPGB, while FNGB has the poorest MIA. The trend is highlighted by the comparison of the MIA ranges, and also by the comparison of the MIA of corresponding
complexes. The comparison of the complexes with Cu binding to O14 is the most