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Synthesis and Structure of Linear and Cyclic Oligomers of 3‐Hydroxybutanoic Acid with Specific Sequences of ( R )‐ and ( S )‐Configurations
Author(s) -
Bachmann Beat M.,
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/(sici)1522-2675(19981216)81:12<2430::aid-hlca2430>3.0.co;2-w
Subject(s) - chemistry , cyclic peptide , stereochemistry , combinatorial chemistry , biochemistry , peptide
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 H 2 / Noyori‐Taber catalyst ( Scheme 2 ). The HB building blocks were then protected ( 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, 1 H‐ and 13 C‐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.