Carbocyclic Substrate Analogues Reveal Kanosamine Biosynthesis Begins with the α-Anomer of Glucose 6-Phosphate

Operationally simple enzymatic deprotection of C-3 position on 3,4,6-tri-O-acetyl-d-glucal

The new strategies to obtain selectively protected hydroxyl function on sugar derivatives are still of the high value for the progress of glycochemistry and organic synthesis. Herein, we describe an interesting enzymatic deprotection strategy that was applied to the most commonly used glycal derivative - 3,4,6-tri-O-acetyl-d-glucal. The procedure is operationally simple, easy to scale-up and the biocatalyst might be effortlessly recycled from the reaction mixture. Resulting product - 4,6-di-O-acetyl-D-glucal we then challenged to synthesize two glycal synthons armed with 3 different protecting group - a synthetic target difficult to achieve with traditional methods.

Simultaneous Broadband Suppression of Homonuclear and Heteronuclear Couplings in 1 H NMR Spectroscopy

The ¹ H NMR analysis of species containing NMR-active heteronuclei can be difficult due to signal overlap caused by the combined effects of homonuclear and heteronuclear scalar (J) couplings. Here, a general pure shift method is presented for obtaining ultra-high resolution ¹ H NMR spectra where spectral overlap is drastically reduced by suppressing both homonuclear and heteronuclear J-couplings, giving one single signal per ¹ H chemical environment. Its usefulness is demonstrated in the analysis of fluorine- and phosphorus-containing compounds of pharmaceutical and biochemical interest.

Substrate Substitution in Kanosamine Biosynthesis Using Phosphonates and Phosphite Rescue

Kanosamine is an antibiotic and antifungal compound synthesized from glucose 6-phosphate (G6P) in Bacillus subtilis by the action of three enzymes: NtdC, which catalyzes NAD-dependent oxidation of the C3-hydroxyl; NtdA, a PLP-dependent aminotransferase; and NtdB, a phosphatase. We previously demonstrated that NtdC can also oxidize substrates such as glucose and xylose, though at much lower rates, suggesting that the phosphoryloxymethylene moiety of the substrate is critical for effective catalysis. To probe this, we synthesized two phosphonate analogues of G6P in which the bridging oxygen is replaced by methylene and difluoromethylene groups. These analogues are substrates for NtdC, with second-order rate constants an order of magnitude lower than those for G6P. NtdA converts the resulting 3-keto products to the corresponding kanosamine 6-phosphonate analogues. We compared the rates to the rate of NtdC oxidation of glucose and xylose and showed that the low reactivity of xylose could be rescued 4-fold by the presence of phosphite, mimicking G6P in two pieces. These results allow the evaluation of the individual energetic contributions to catalysis of the bridging oxygen, the bridging C6 methylene, the phosphodianion, and the entropic gain of one substrate versus two substrate pieces. Phosphite also rescued the reversible formation 3-amino-3-deoxy-d-xylose by NtdA, demonstrating that truncated and nonhydrolyzable analogues of kanosamine 6-phosphate can be generated enzymatically.