1.1-Acetyl-3-[(3R)-hydroxyfatty acyl]-glycerols: lipid compounds from Euphrasia rostkoviana Hayne and E. tetraquetra (Bréb.) Arrond.
Lorenz P1, Knittel DN1, Conrad J2, Lotter EM3, Heilmann J3, Stintzing FC1, Kammerer DR1. Chem Biodivers. 2016 Apr 3. doi: 10.1002/cbdv.201500233. [Epub ahead of print]
Five homologous acetylated acylglycerols of 3-hydroxyfatty acids (chain lengths C14 -C18 ), named euphrasianins A-E, were characterized for the first time in Euphrasia rostkoviana Hayne (Orobanchaceae) by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MSn ). In addition to mass spectrometric data, structures of euphrasianins were verified via a three-step total synthesis of one representative homologue (euphrasianin A). The structure of the latter was confirmed by 1D and 2D NMR experiments as well as high resolution electrospray ionization-mass spectrometry (HR-ESI-MS). The absolute configuration of the 3-hydroxyfatty acid moiety at C(3) was found to be R in the natural euphrasianins, which was determined by alkaline hydrolysis and methylation of a purified fraction, followed by chiral GC analysis. Furthermore, in extracts of E.
2.Identification of β-phenylalanine as a non-protein amino acid in cultivated rice, Oryza sativa.
Yokoo T1, Takata R1, Yan J2, Matsumoto F1, Teraishi M1, Okumoto Y1, Jander G3, Mori N1. Commun Integr Biol. 2015 Sep 25;8(5):e1086045. doi: 10.1080/19420889.2015.1086045.
Non-protein amino acids, often analogs of the standard 20 protein amino acids, have been discovered in many plant species. Recent research with cultivated rice (Oryza sativa) identified (3R)-β-tyrosine, as well as a tyrosine amino mutase that synthesizes (3R)-β-tyrosine from the protein amino acid (2S)-α-tyrosine. Gas chromatography-mass spectrometry (GC-MS) assays and comparison to an authentic standard showed that β-phenylalanine is also a relatively abundant non-protein amino acid in rice leaves and that its biosynthesis occurs independently from that of β-tyrosine.
3.Absolute Stereochemistry of the β-Hydroxy Acid Unit in Hantupeptins and Trungapeptins.
Gupta DK, Ding GC, Teo YC, Tan LT. Nat Prod Commun. 2016 Jan;11(1):69-72.
The β-hydroxy/amino acid unit is a common structural feature of many bioactive marine cyanobacterial depsipeptides. In this study, the absolute stereochemistry of the β-hydroxy acid moieties in hantupeptins and trungapeptins were determined through their synthesis and HPLC analysis of the Mosher ester derivatives. Synthesis of two3-hydroxy-2-methyloctanoic acid (Hmoa) stereoisomers, (2S,3R)-Hmoa and (2S,3S)-Hmoa, were achieved using diastereoselective asymmetric method and the retention times of all four Hmoa isomers were established indirectly by RPLC-MS analysis of their Mosher ester derivative standards. Based on the retention times of the standards, the absolute configuration of the Hmoa unit in hantupeptin C (3) and trungapeptin C (6) was assigned as (2R,3S)- and (2S,3R)-Hmoa, respectively. The use of the Mosher's reagents, coupled with HPLC analysis, provided a viable alternative to the absolute stereochemical determination of β-hydroxy acid units in depsipeptides.
4.Asymmetric Synthesis and Binding Study of New Long-Chain HPA-12 Analogues as Potent Ligands of the Ceramide Transfer Protein CERT.
Ďuriš A1, Daïch A2, Santos C3, Fleury L4, Ausseil F4, Rodriguez F3, Ballereau S3, Génisson Y5, Berkeš D6. Chemistry. 2016 Mar 31. doi: 10.1002/chem.201505121. [Epub ahead of print]
A series of 12 analogues of the Cer transfer protein (CERT) antagonist HPA-12 with long aliphatic chains were prepared as their (1R,3S)-syn and (1R,3R)-anti stereoisomers from pivotal chiral oxoamino acids. The enantioselective access to these intermediates as well as their ensuing transformation relied on a practical crystallization-induced asymmetric transformation (CIAT) process. Sonogashira coupling followed by triple bond reduction and thiophene ring hydrodesulfurization (HDS) into the corresponding alkane moieties was then implemented to complete the synthetic routes delivering the targeted HPA-12 analogues in concise 4- to 6-step reaction sequences. Ten compounds were evaluated regarding their ability to bind to the CERT START domain by using the recently developed time-resolved FRET-based homogeneous (HTR-FRET) binding assay. The introduction of a lipophilic appendage on the phenyl moiety led to an overall 10- to 1000-fold enhancement of the protein binding, with the highest effect being observed for a n-hexyl residue in the meta position.
