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Synthesis and Properties of Monodisperse Chiral Dendrimers (up to Fourth Generation) with doubly branched building blocks : An intriguing solvent effect
Author(s) -
Murer Peter,
Seebach Dieter
Publication year - 1998
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19980810313
Subject(s) - dendrimer , chemistry , dispersity , stereocenter , circular dichroism , solvent , branching (polymer chemistry) , optical rotation , specific rotation , crystallography , stereochemistry , polymer chemistry , organic chemistry , enantioselective synthesis , catalysis
‘Fully chiral’ dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units ( cf. 27 ) and chiral branch diols ( cf. 8 , 12 , and 24 ) as building blocks. The biggest dendrimer prepared is of the 4th generation ( 33 : 46 building blocks, 93 stereogenic centers, 10 28 possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[( R )‐3‐hydroxybutanoic acid] (P(3‐HB)). All compounds were shown to be monodisperse by MALDI‐TOF mass spectrometry. Spin‐lattice relaxation‐time ( T 1 ) measurements and size‐exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chiral building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent ( cf. Fig. 13 ).