L-Glutamic acid γ-cyclohexyl ester

We disclose the first synthesis of the marine natural product, (+)-boneratamide A, whose structure is composed of a terpene unit linked via an amide bond to a pyroglutamic acid moiety. The key step in this route is a bioinspired Ugi reaction of (+)-axisonitrile-3 with acetone as the carbonyl component and L-glutamic acid. This reaction brings about a remarkably efficient, one-pot assembly of reaction components concomitant with γ-lactam ring formation to produce (+)-boneratamide A in 70% yield. (+)-Boneratamide B and (-)-boneratamide C methyl esters were also synthesized using a similar bioinspired strategy, and the relative stereochemistries at the stereogenic centers in these substances were elucidated using X-ray analysis.

Corynebacterium glutamicum is a biotin auxotroph that secretes L-glutamic acid in response to biotin limitation; this process is employed in industrial L-glutamic acid production. Fatty acid ester surfactants and penicillin also induce L-glutamic acid secretion, even in the presence of biotin. However, the mechanism of L-glutamic acid secretion remains unclear. It was recently reported that disruption of odhA, encoding a subunit of the 2-oxoglutarate dehydrogenase complex, resulted in L-glutamic acid secretion without induction. In this study, we analyzed odhA disruptants and found that those which exhibited constitutive L-glutamic acid secretion carried additional mutations in the NCgl1221 gene, which encodes a mechanosensitive channel homolog. These NCgl1221 gene mutations lead to constitutive L-glutamic acid secretion even in the absence of odhA disruption and also render cells resistant to an L-glutamic acid analog, 4-fluoroglutamic acid. Disruption of the NCgl1221 gene essentially abolishes L-glutamic acid secretion, causing an increase in the intracellular L-glutamic acid pool under biotin-limiting conditions, while amplification of the wild-type NCgl1221 gene increased L-glutamate secretion, although only in response to induction. These results suggest that the NCgl1221 gene encodes an L-glutamic acid exporter. We propose that treatments that induce L-glutamic acid secretion alter membrane tension and trigger a structural transformation of the NCgl1221 protein, enabling it to export L-glutamic acid.

γ-PGA-NHS ester, which was prepared using poly(γ-glutamic acid) (γ-PGA) and N-hydroxysuccinimide (NHS) as the raw materials, was synthesized to be a novel cross-linker of collagen. Fourier transform infrared spectra analysis suggested that the products displayed the characteristic absorption peak of ester. Results from nuclear magnetic resonance analysis indicated that the esterification degree of γ-PGA-NHS ester was increased with the increase of NHS. Modified collagen was prepared and characterized. The results of circular dichroism analysis indicated modified collagen retained the triple helix structure of natural collagen. Sodium dodecyl sulphate polyacrylamide gel electrophoresis revealed that the molecular weight of collagen was increased after cross-linking. Peptide mapping of collagen suggested that cross-linked collagen possessed an enhanced resistance to trypsin degradation. Differential scanning calorimeter results showed that the denaturation temperature of collagen was improved from 68.1±0.4 to 91.2±0.5°C (p<0.05). Dynamic viscoelastic measurements demonstrated the improvement of thermal stability and reflected the exponential increase in η*. The cross-linked collagen retained porous structure and the pore size became larger as observed by scanning electron microscopy. The investigation results provided useful information to produce collagen with improved physicochemical properties, particularly the thermal stability via the use of γ-PGA-NHS ester as a biomacromolecule-based cross-linker.