15 Creation of Molecularly Integrated Multi-responsive …
263
Table 15.1 Enantioselectivity
of diarylethenes in HSA in
different media composition
incubated at 25 °C
MeCN in PBS (vol) (%) Ee values/%
7c
8c
9c
1
28
33
27
5
50
40
72
10
76
44
92
15
80 (94) a
48 (56) a
94 (>99) a
20
74
40
91
Reproduced from Ref. [29] with permission from the Royal Society
of Chemistry
a Ee values in parentheses are those when incubated at −4 °C
formed in HSA to be (S,S)-5c by X-ray crystallographic analysis of a derivative.
Since the basic molecular skeleton of 8c and 9c is common to 5c, we undertook the
transformation experiments between 5c, 8c and 9c.
Although it seemed easy, the correlation between 5c and 8c was very difficult to establish. Oxidation of optically resolved 5c with various oxidizing agents
failed. The reduction of 9c was also unsuccessful. Only one successful transformation was the borane reduction of 8c to 5c. Esterification of 8c or the hydrolysis of 9c by acid- or base-catalyzed reactions also failed. Esterification of 8c by
trimethylsilyldiazomethane was the only way to connect 8c with 9c.
As a result, it was concluded that the main enantiomer of 8c is (R,R)-8c and
the main enantiomer of 9c is (S,S)-9c. The transformation pathways, the absolute
stereochemistry of the major and minor enantiomers obtained in HSA and the their
properties related to their behavior in the HPLC and CD spectra are all shown in
Chart 15.6 [29].
15.3.5 Section Conclusion
The enantioselective ring closure of diarylethenes incorporated in HSA and the determination of the absolute stereochemistry of the major enantiomers were carried out
[29]. Since HSA is a peptide made of chiral amino acids, the transfer of chirality
from HSA to the diarylethene molecules during photochemical electrocyclization
was efficiently achieved. Since diarylethenes are photochromic, repeated generation
and extinction of the chiral molecules on demand are now possible.
It is noteworthy that since serum albumin is a water-soluble peptide which has no
particular activities as an enzyme and just transports water-insoluble materials, serum
albumin can convey water-insoluble photochromic molecules to any area within an
animal through the blood vessels as molecularly isolated forms.
263
Table 15.1 Enantioselectivity
of diarylethenes in HSA in
different media composition
incubated at 25 °C
MeCN in PBS (vol) (%) Ee values/%
7c
8c
9c
1
28
33
27
5
50
40
72
10
76
44
92
15
80 (94) a
48 (56) a
94 (>99) a
20
74
40
91
Reproduced from Ref. [29] with permission from the Royal Society
of Chemistry
a Ee values in parentheses are those when incubated at −4 °C
formed in HSA to be (S,S)-5c by X-ray crystallographic analysis of a derivative.
Since the basic molecular skeleton of 8c and 9c is common to 5c, we undertook the
transformation experiments between 5c, 8c and 9c.
Although it seemed easy, the correlation between 5c and 8c was very difficult to establish. Oxidation of optically resolved 5c with various oxidizing agents
failed. The reduction of 9c was also unsuccessful. Only one successful transformation was the borane reduction of 8c to 5c. Esterification of 8c or the hydrolysis of 9c by acid- or base-catalyzed reactions also failed. Esterification of 8c by
trimethylsilyldiazomethane was the only way to connect 8c with 9c.
As a result, it was concluded that the main enantiomer of 8c is (R,R)-8c and
the main enantiomer of 9c is (S,S)-9c. The transformation pathways, the absolute
stereochemistry of the major and minor enantiomers obtained in HSA and the their
properties related to their behavior in the HPLC and CD spectra are all shown in
Chart 15.6 [29].
15.3.5 Section Conclusion
The enantioselective ring closure of diarylethenes incorporated in HSA and the determination of the absolute stereochemistry of the major enantiomers were carried out
[29]. Since HSA is a peptide made of chiral amino acids, the transfer of chirality
from HSA to the diarylethene molecules during photochemical electrocyclization
was efficiently achieved. Since diarylethenes are photochromic, repeated generation
and extinction of the chiral molecules on demand are now possible.
It is noteworthy that since serum albumin is a water-soluble peptide which has no
particular activities as an enzyme and just transports water-insoluble materials, serum
albumin can convey water-insoluble photochromic molecules to any area within an
animal through the blood vessels as molecularly isolated forms.