Synthesis and Structure of Linear and Cyclic Oligomers of 3-Hydroxybutanoic Acid with Specific Sequences of (R)- and (S)-Configurations

Bachmann, Beat M.; Seebàch, Dieter

doi:10.1002/(sici)1522-2675(19981216)81:12<2430::aid-hlca2430>3.0.co;2-w

Cited by 33 publications

(21 citation statements)

References 16 publications

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“…While the enantiomerically pure building blocks required for these oligomers were obtained by hydrolysis of the biopolymer PHB/PHV [29], b-hydroxy acid derivatives with substituents other than Me or Et in the b-position had to be prepared by enantioselective synthesis. The methodology (Scheme 1) chosen for that purpose, i.e., hydrogenation of b-keto esters 9 ) with the Noyori catalyst [Ru((R)-binap)Cl 2 ] [31] has previously been used by us for the preparation of (S)-3-hydroxybutyrate [16]. The Rubinap catalyst was prepared in situ, according to a procedure by Gene√t et al [32], and the hydrogenation of b-keto esters 4 and 5 was carried out under 100 atm H 2 pressure at ambient temperature to yield the products 6 and 7, respectively, with enantiomer purities above 98% 10 ) in essentially quantitative yield.…”

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confidence: 76%

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Synthesis and NMR Analysis in Solution of Oligo(3-hydroxyalkanoic acid) Derivatives with the Side Chains of Alanine, Valine, and Leucine (β-Depsides): Coming Full Circle from PHB toβ-Peptides to PHB

Albert

Seebàch

Duchardt

et al. 2002

HCA

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Oligomers of 3-hydroxyalkanoic acids that contain two, three, and six residues with and without O-terminal (tBu)Ph 2 Si and C-terminal PhCH 2 protection have been synthesized in such a way that the side chains on the oligoester backbone were those of the proteinogenic amino acids Ala (Me), Val (CHMe 2 ), and Leu (CH 2 CHMe 2 ). The enantiomerically pure 3-hydroxyalkanoates were obtained by Noyori hydrogenation of the corresponding 3-oxo-alkanoates with [Ru((R)-binap)Cl 2 ](binap 2,2'bis(diphenylphosphanyl)-1,1'-binaphthalene)/H 2 (Scheme 1), and the coupling was achieved under the conditions (pyridine/(COCl) 2 , CH 2 Cl 2 , À 788) previously employed for the synthesis of various oligo(3-hydroxybutanoic acids) (Schemes 2 and 3). The Cotton effects in the CD spectra of the new oligoesters provided no hints about chiral conformation (cf. a helix) in MeOH, MeCN, octan-1-ol, or CF 3 CH 2 OH solutions (Figs. 1 and 2). Detailed NMR investigations in CDCl 3 solution (Figs. 3 ± 6, and Tables 1 ± 5) of the hexa(3-hydroxyalkanoic acid) with the side chains of Val (HC), Ala (HB), Leu (HH), Val, Ala, Leu (from O-to C-terminus; 3) gave, on the NMR time-scale, no evidence for the presence of any significant amount of a 2 1 -or a 3 1 -helical conformation, comparable to those identified in stretched fibers of poly[(R)-3-hydroxybutanoic acid], or in lamellar crystallites and in single crystals of linear and cyclic oligo[(R)-3-hydroxybutanoic acids], or in the corresponding b-peptide(s) (the oligo(3-aminoalkanoic acid) analogs; 1 ± 3). Thus, the extremely high flexibility (averaged or −random-coil× conformation) of the polyester chain (COÀO rotational barrier ca. 13 kcal/mol; no hydrogen bonding), as compared to polyamide chains (COÀNH barrier ca. 18 kcal/mol; hydrogen bonding) has been demonstrated once again. The possible importance of this structural flexibility, which goes along with amphiphilic properties, for the role of PHB in biology, in evolution, and in prebiotic chemistry is discussed. Structural similarities of natural potassiumchanneling proteins and complexes of oligo(3-hydroxybutanoates) with Na , K , or Ba 2 are alluded to (Figs. 7 ± 9).1. Indroduction. ± The short-chain version of poly[(R)-3-hydroxybutanoic acid] (c-PHB), 1, has been detected in numerous biological systems, and we believe that it is fair to say that the biopolymer PHB is present in all living organisms 3 ). The low-molecularweight PHB has been shown to cause phospholipid membranes to become permeable for cations, such as Na, K, Rb, Ca or Ba, under voltage-driven (patch-clamp experiments [5]) and under concentration-driven (artificial vesicles [6]) conditions. Furthermore, a Ca polyphosphate-PHB complex consisting of ca. 140 HB and 70 phosphate units and containing ca. 35 Ca 2 ions has been identified as a Ca-specific ion Helvetica Chimica Acta ± Vol. 85 (2002) 633 1 ) Part of the projected Ph. D. Theses of M. A. and E. D., ETH-Z¸rich and MIT, respectively.

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confidence: 76%

“…9) 15 ). Recent synthetic model chemistry of the potassium channel in combination with NMR spectroscopy, indeed, suggest cooperative forming and breaking of four H-bonds in the channel to accomodate ion passage through the filter [49] 16 ).…”

Section: Roementioning

confidence: 99%

Synthesis and NMR Analysis in Solution of Oligo(3-hydroxyalkanoic acid) Derivatives with the Side Chains of Alanine, Valine, and Leucine (β-Depsides): Coming Full Circle from PHB toβ-Peptides to PHB

Albert

Seebàch

Duchardt

et al. 2002

HCA

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“…5. Finally, we note that Bachmann and Seebach (14) have reported the preparation and characterization of cyclic lactones (MeCHCH 2 C(O)O) n , where n ϭ 4 and 8.…”

Section: Brunelle and Coworkers (9) At Ge Corporate Research Andmentioning

confidence: 90%

Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Chisholm

Gallucci

Yin

2006

Proc. Natl. Acad. Sci. U.S.A.

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The reaction between Bu n Li in benzene and the solid polystyrene support PS-C 6H4CH2NH2 leads to a lithiated species that can be represented as PS-C 6H4CH2NHLi(LiBu)x, where x ϳ 4, which is active in the ring-opening of the cyclic esters L-lactide, rac-lactide, and 2,5-morpholinediones. With Ϸ10 eq of these monomeric six-membered rings and with heating, cyclic esters (MeCHC ( dynamic combinatorial library ͉ ring enlarging T he ring-opening polymerization of cyclic esters such as lactides (LA) is a well established procedure for the production of polyesters (1). This is commonly brought about by the use of metal catalyst precursors, although organic catalysis is possible by employing a nucleophilic base such as 4-dimethyl aminopyridine or an N-heterocyclic carbene with alcohol initiators (2-5). It is now generally accepted that metal-alkoxide species are the key reactive intermediates in the propagation steps and, furthermore, that these, too, play a role in the competing side reactions of transesterification and chain transfer (6). These reactions are collectively shown in Scheme 1.Transesterification is normally a deleterious side reaction because it leads to a loss of control of molecular mass in a living polymerization and, because in a stereoselective ring-opening polymerization, transesterification scrambles the stereocenters along a chain. As shown in Scheme 1, transesterification can occur by a bimolecular mechanism or a reaction involving a single chain. The latter reaction, intrachain transesterification leads to cycles. Previously, we found that the polymerization of lactide by Ph 2 SnX 2 initiators, where X ϭ OPr i or NMe 2 , gave different ratios of chains to cycles with the cycles being significantly more prominent for X ϭ NMe 2 . This apparently arises because of the favorable chelation of the SnOCHMeC(O)NMe 2 groups (7).Prompted by these observations, we set out to explore a synthetic route for cyclic oligoesters derived from LA and we describe herein our findings. It is worthy of mention that others have synthesized cyclic esters and carbonates principally as a route for the formation of polyesters and polycarbonates (8). Brunelle and coworkers (9) at GE Corporate Research andDevelopment specifically developed high-yielding syntheses of cyclic esters derived from 1,4-aromatic acyl chlorides and diols. These ringed compounds melt to yield low viscous media, which by a thermo-neutral ring-opening polymerization give polyesters with no elimination products. This chemistry forms the technology platform of Cyclics Corporation. 2. Kricheldorf and coworkers (10, 11) have used principally tin(IV) diolates as initiators for the ring-opening polymerization and the reaction with dicarboxylic acid chlorides to cleave the cyclic esters. 3. Hodge and coworkers (12) used a solid support and step growth polymerization to produce a polyester chain followed by treatment with a metal catalyst, most often Bu n 2 SnO, to affect intrachain transesterification and release of the cyclic esters to the solution phase. 4....

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“…(c ¼ 1:0 in MeOH), 6) and the HB4 we have isolated showed a levorotatory (½ D À12 , c ¼ 0:65 in MeOH). Considering these features together, it is concluded that all of the four chiral carbons of HB4 produced by EC-K085 are in the R-configuration.…”

Section: ) Bachmann and Seebach Have Also Reported Optical Rotation mentioning

confidence: 99%

“…Accordingly, the active principle was found to be a linear-type 3-hydroxybutyrate tetramer (HB4), of which 1 H-and 13 C-NMR chemical shifts were found to be in good accordance with those of authentic (R,R,R,R)-HB4, as previously reported by Bachmann and Seebach. 6) Poly-3-hydroxybutyrate (PHB, also a synonym of -hydroxybutyrate polymer or 3-hydroxybutyrate polymer) is one of the most representative bacterial polymeric substances for several free-living nitrogen-fixing bacteria. Poly-3-hydroxybutyrate depolymerase (PHBDP), which catalyzes endo-type hydrolysis of PHB to produce several linear-type 3-hydroxybutyrate oligomers, including HB4, is also produced by many soil bacteria.…”

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Linear 3-Hydroxybutyrate Tetramer (HB4) Produced bySphingomonassp. Is Characterized as a Growth Promoting Factor for Some Rhizomicrofloral Composers

Ogita

Hashidoko

Limin

et al. 2006

Bioscience, Biotechnology, and Biochemistry

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Synthesis and Structure of Linear and Cyclic Oligomers of 3-Hydroxybutanoic Acid with Specific Sequences of (R)- and (S)-Configurations

Cited by 33 publications

References 16 publications

Synthesis and NMR Analysis in Solution of Oligo(3-hydroxyalkanoic acid) Derivatives with the Side Chains of Alanine, Valine, and Leucine (β-Depsides): Coming Full Circle from PHB toβ-Peptides to PHB

Synthesis and NMR Analysis in Solution of Oligo(3-hydroxyalkanoic acid) Derivatives with the Side Chains of Alanine, Valine, and Leucine (β-Depsides): Coming Full Circle from PHB toβ-Peptides to PHB

Cyclic esters and cyclodepsipeptides derived from lactide and 2,5-morpholinediones

Linear 3-Hydroxybutyrate Tetramer (HB4) Produced bySphingomonassp. Is Characterized as a Growth Promoting Factor for Some Rhizomicrofloral Composers

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