165054-82-0Relevant academic research and scientific papers
Synthesis of Linear Oligomers of (R)-3-Hydroxybutyrate and Solid-State Structural Investigations by Electron Microscopy and X-Ray Scattering
Seebach, Dieter,Buerger, H. Michael,Mueller, Hans-Martin,Lengweiler, Urs D.,Beck, Albert K.,et al.
, p. 1099 - 1123 (1994)
Repetitive treatment of the biopolymer P(3-HB) (molecular weight > 105 Dalton, storage or s-P(3-HB)), with lithium hexamethyl disilazanid (LHMDS) at -70 deg in THF leads to a mixture of oligomers with increasingly sharp distribution around a 15-, 30-, and 45mer.Discrete fragments are also isolated when P(3-HB) is heated under reflux (89 deg) in neat Et3N.Linear oligo(3-HB) derivatives (3-7) containing up to 96 3-HB units are synthesized using an exponential segment-coupling strategy.These oligomers are used to calibrate size-exclusion chromatography columns for the analysis of oligo(3-HB) samples from the different sources.The linear oligo-(3-HB) derivatives also served as a model with respect to the physical properties of high molecular weight P(3-HB) and were investigated as such by transmission electron microscopy (TEM) and by small- and wide-angle X-ray scattering (SAXS and WAXS).The thicknesses of the lamellar crystallites (long periods) formed by the 8mer, 16mer, and 32mer, are ca. 26, 52, and 53 Angstroem, respectively, indicating that the 32mer molecules are folded once, very tightly, into a 'hair-pin'-type conformation.High-molecular-weight P(3-HB), which was crystallized in a similar way, also has a lamellar crystallite thickness of ca. 50-65 Angstroem.Thus, the treatment of P(3-HB) with LHMDS at low temperature causes etching of the amorphous regions, an effect well known in polymer science for studying the regularity of chain folding.The ca. 50-Angstroem packing within the tight folds of P(3-HB) is discussed in view of its possible function in ion transport through cell membranes.
Synthesis and structure of linear and cyclic oligomers of 3- hydroxybutanoic acid with specific sequences of (R)- and (S)-configurations
Bachmann, Beat M.,Seebach, Dieter
, p. 2430 - 2461 (2007/10/03)
To study the stereoselectivity of enzymatic cleavage of poly(3- hydroxybutyrates) (PHB) in a well-defined system (purified depolymerase and monodisperse substrate of specific relative configuration), linear and cyclic oligomers of HB (OHBs) containing (R)- and (S)-3-hydroxybutanoate residues were synthesized. The starting material (R)-HB was prepared from natural sPHB, and (S)-HB by enantioselective reduction of 3- oxobutanoate with yeast or with H2/Noyori-Taber catalyst (Scheme2). The HB building blocks were then prolected (O-benzyl/tert-butyl ester; Scheme 3) and coupled to give dimers 3, 4, tetramers 5-9, and octamers 10-18; for analytical comparison, a 3mer, 5mer, 6mer, and 7mer (19-22) were also prepared. Two of the tetramers were subjected to macrolactonization conditions (Yamaguchi) to give the cyclic tetramers 23 and 25 and octamers 24 and 26. All new compounds were fully characterized (m.p., [α](D), CD, IR, 1H- and 13C-NMR, MS, elemental analysis). Single-crystal X-ray structure analyses were performed with oligolides 24 and 25 (Figs. 2 and 4), and the structures, as well as the crystal packing, were compared with those of analogs containing only (R)-HB units or consisting of 3-amino- instead of 3-hydroxybutanoic-acid moieties.
