Photoselective synthesis of azobenzene-containing cyclic oligosarcosine and its thermal cis → trans isomerization in solution

✍ Scribed by Masahiko Sisido; Hiroshi Ito; Yukio Imanishi

• Publisher: Wiley (John Wiley & Sons)
• Year: 1982
• Tongue: English
• Weight: 682 KB
• Volume: 21
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360210810

✦ Synopsis

Abstract

Oligosarcosines, which contain as azobenzene group at the center of the chain and amino groups at both ends [(Sar)~n~Azo(Sar)~n~], were prepared with the N‐carboxyanhydride method. The oligomers were coupled with an equimolar amount of succinyl chloride in the presence of triethylamine. When the condensation was carried out under photo irradiation, the azobenzene group assumed the cis configuration and the intramolecular reaction (cyclization) was facilitated. Intermolecular polycondensation occurred preferentially in the dark, in which case the azo group was trans. Cyclic oligosarcosine, which contains one azo group, was isolated by gel chromatography, and its thermal cis → trans isomerization was examined in dimethylformamide. The isomerization rate depended strongly on the number of sarcosine units n in the oligomer; for very small rings (n < 5), the rate constants were less than those for open‐chain analogs; for rings of medium size (n = 5 ∼ 10), they were larger than those for open‐chain analogs; and for longer chains, no significant difference was observed. This specific chain‐length dependence was explained by the conformational restrictions of the cyclic oligomers. The ring‐restricted isomerization was evidenced by an isomerization‐induced conformational change observed in ^1^H‐nmr spectroscopy.