188
M. K. Bilonda and L. Mammino
Table 1 Letters used in the acronyms denoting the conformers of shuangancistrotectorine A in
this work, and their meanings
Letter Meaning
Letter Meaning
a
Presence of the O43–H52···O42 IHB u
Presence of the C–H56···O43 IHB
b
Presence of the O44–H54···O45 IHB t
C14–C13–C21–C28 torsion angle
close to +90°
c
Presence of the O43–H52···π IHB
v
C14–C13–C21–C28 torsion angle
close to −90°
d
Presence of the O44–H54···π IHB
p
C4–C5–C11–C12 torsion angle close
to +90°
g
Presence of the C–H49···O41 IHB
q
C4–C5–C11–C12 torsion angle close
to −90°
h
Presence of the C–H59···O46 IHB
x
C22–C23–C31–C38 torsion angle
close to 90°
i
Presence of the C–H53···O44 IHB
y
C22–C25–C31–C38 torsion angle
close to −90°
The following example illustrates how the acronyms describe the characteristics of individual conformers. In the SHA-1-a-b-g-h-i-u-q-v-x acronym, ‘1’ represent the first position in order of increasing relative energy (i.e., the lowest
energy conformer); ‘a’ and ‘b’ represent the O–H···O IHBs present (O43–H52···O44
and O44–H54···O45); ‘g,h,i,u’ represent the C–H···O interactions present (C–
H49···O41, C–H59···O46, C–H53···O44 and C–H56···O43); and ‘q-v-x’ inform that
the C4 C5 C11 C12 torsion angle is close to −90° (q), the C14 C13 C21 C28 torsion angle is close to −90° (v) and the C22–C23–C31–C38 torsion angle is close to
90° (x). In the text, the acronyms denoting the conformers start with ‘SHA’, whereas
in the tables and figures ‘SHA’ is not reported for the sake of space-saving and the
conformers are indicated only by the number and series of letters denoting their
characteristics.
Since it is convenient to be able to mention each ring individually and concisely,
the rings are denoted by uppercase letters. Since the two units are identical, identical
rings are denoted by the same letters, priming those of one of the units (A, B, C,
D, A
, B
, C
and D
, Fig. 1). The whole unit comprising the A, B, C and D rings is
called S and the whole unit comprising the A
, B
, C
and D
rings is called S
. This
option to denote rings and units had initially been designed for JZM [4].
3.2 Results in Vacuo
16 conformers were identified and the frequency calculations confirm that they are
true minima. Figure 2 shows their geometries and Table 2 reports their relative energies from HF and DFT results. Although it is known that the molecule is symmetric,
some pairs of symmetric conformers were calculated independently to verify how
M. K. Bilonda and L. Mammino
Table 1 Letters used in the acronyms denoting the conformers of shuangancistrotectorine A in
this work, and their meanings
Letter Meaning
Letter Meaning
a
Presence of the O43–H52···O42 IHB u
Presence of the C–H56···O43 IHB
b
Presence of the O44–H54···O45 IHB t
C14–C13–C21–C28 torsion angle
close to +90°
c
Presence of the O43–H52···π IHB
v
C14–C13–C21–C28 torsion angle
close to −90°
d
Presence of the O44–H54···π IHB
p
C4–C5–C11–C12 torsion angle close
to +90°
g
Presence of the C–H49···O41 IHB
q
C4–C5–C11–C12 torsion angle close
to −90°
h
Presence of the C–H59···O46 IHB
x
C22–C23–C31–C38 torsion angle
close to 90°
i
Presence of the C–H53···O44 IHB
y
C22–C25–C31–C38 torsion angle
close to −90°
The following example illustrates how the acronyms describe the characteristics of individual conformers. In the SHA-1-a-b-g-h-i-u-q-v-x acronym, ‘1’ represent the first position in order of increasing relative energy (i.e., the lowest
energy conformer); ‘a’ and ‘b’ represent the O–H···O IHBs present (O43–H52···O44
and O44–H54···O45); ‘g,h,i,u’ represent the C–H···O interactions present (C–
H49···O41, C–H59···O46, C–H53···O44 and C–H56···O43); and ‘q-v-x’ inform that
the C4 C5 C11 C12 torsion angle is close to −90° (q), the C14 C13 C21 C28 torsion angle is close to −90° (v) and the C22–C23–C31–C38 torsion angle is close to
90° (x). In the text, the acronyms denoting the conformers start with ‘SHA’, whereas
in the tables and figures ‘SHA’ is not reported for the sake of space-saving and the
conformers are indicated only by the number and series of letters denoting their
characteristics.
Since it is convenient to be able to mention each ring individually and concisely,
the rings are denoted by uppercase letters. Since the two units are identical, identical
rings are denoted by the same letters, priming those of one of the units (A, B, C,
D, A
, B
, C
and D
, Fig. 1). The whole unit comprising the A, B, C and D rings is
called S and the whole unit comprising the A
, B
, C
and D
rings is called S
. This
option to denote rings and units had initially been designed for JZM [4].
3.2 Results in Vacuo
16 conformers were identified and the frequency calculations confirm that they are
true minima. Figure 2 shows their geometries and Table 2 reports their relative energies from HF and DFT results. Although it is known that the molecule is symmetric,
some pairs of symmetric conformers were calculated independently to verify how