H. Wilde

White biotechnology for green chemistry: fermentative 2-oxocarboxylic acids as novel building blocks for subsequent chemical syntheses

Functionalized compounds, which are difficult to produce by classical chemical synthesis, are of special interest as biotechnologically available targets. They represent useful building blocks for subsequent organic syntheses, wherein they can undergo stereoselective or regioselective reactions. “White Biotechnology” (as defined by the European Chemical Industry [http://www.europabio.org/white_biotech.htm], as part of a sustainable “Green Chemistry,”) supports new applications of chemicals produced via biotechnology. Environmental aspects of this interdisciplinary combination include: Use of renewable feedstockOptimization of biotechnological processes by means of: New “high performance” microorganismsOn-line measurement of substrates and products in bioreactorsAlternative product isolation, resulting in higher yields, and lower energy demand In this overview we describe biotechnologically produced pyruvic, 2-oxopentaric and 2-oxohexaric acids as promising new building blocks for synthetic chemistry. In the first part, the microbial formation of 2-oxocarboxylic acids (2-OCAs) in general, and optimization of the fermentation steps required to form pyruvic acid, 2-oxoglutaric acid, and 2-oxo-d-gluconic acid are described, highlighting the fundamental advantages in comparison to chemical syntheses. In the second part, a set of chemical formula schemes demonstrate that 2-OCAs are applicable as building blocks in the chemical synthesis of, e.g., hydrophilic triazines, spiro-connected heterocycles, benzotriazines, and pyranoic amino acids. Finally, some perspectives are discussed.

N-Glycosidation of D-arabino-hex-2-ulosonic acid.

Two approaches to N-functionalized D-arabino-hex-2-ulosonic acid derivatives were established by nucleophilic substitution of methyl (3,4,5-tri-O-acetyl-beta-D-arabino-hex-2-ulopyranosyl)onate bromide (1). Reaction of 1 with amino compounds in the presence of mercury(II) cyanide led to the 2,3-cis configured beta-D-arabino N-glycosides. On the other hand, the reaction of bromide 1 with azide, followed by catalytic hydrogenation led to 2,3-trans alpha-D-arabino glycosyl amine methyl 3,4,5-tri-O-acetyl-2-amino-alpha-D-arabino-hex-2-ulopyranosonate, which was easily rearranged to the thermodynamically more stable beta-D-arabino N-acetyl derivative methyl 4,5-di-O-acetyl-2-acetylamino-3-hydroxy-beta-D-arabino-hex-2-ulopyranosonate. The assignment of configuration of the tertiary anomeric centre and conformation of all products was based on 1H NMR H,H coupling constants and NOE difference experiments.

Methyl d-arabino-hex-2-ulopyranosonate as a building block for spiro[1,4-benzoxazine-2,2′-pyrans]

Abstract A novel glycosyl donor, methyl (3,4,5-tri- O -acetyl-β- d - arabino -hex-2-ulopyranosyl)onate bromide, obtained in two steps from methyl β- d - arabino -hex-2-ulopyranosonate, was converted into its α-nitrophenyl glycoside, which in turn was reductively cyclized to form acetylated benzoxazinoid spirans. Deprotection led to (2 S )-3′,4,4′,5′-tetrahydroxy- d - arabino -2 H -1,4-benzoxazin-2-spiro-2′-pyran-3(4 H )-one and (2 S )-3′,4′,5′-trihydroxy- d - arabino -2 H -1,4-benzoxazin-2-spiro-2′-pyran-3(4 H )-one. Analogous compounds are prepared from 5-methoxy-2-nitrophenol. The new class of spiro functionalized carbohydrates is structurally related to natural benzoxazinone acetal glucosides. The assignment of configuration and conformation of all products was based on 1 H NMR H,H coupling constants and optical rotation values.

Synthesis of 3,4-dihydropyridazino[1,6-a]benzimidazoles

3,4-Dihydropyridazino[1,6-a]benzimidazoles (4a-e) have been prepared by catalytical hydrogenation of dialkyl (E)-2-(substituted 2-nitrophenyl-hydrazono)glutarates (1a-e) to the respective amines (2) followed by their base catalyzed cyclization in a tandem reaction proceeding via 4,5-dihydropyridazin-6(1H)-one intermediates (3)

Synthesis of spiro[pyrido[3,2-b][1,4]oxazin-2,2′-pyrans] based upon methyld-arabino-2-hexulopyranosonate

Abstract The novel glycosyl donor 1 , derived from methyl d - arabino -2-hexulopyranosonate, was transformed into glycoside 2 , diastereoselectively. Catalytic hydrogenation of 2 and spontaneous reductive cyclization gave access to the spiro[pyrido[3,2- b ][1,4]oxazin-2,2′-pyrans] 3 and 4 .

Hydrazine derivatives of dehydro-l-ascorbic acid

Abstract Condensation of l -threo-2,3-hexodiulosono-1,4-lactone (1) with 2 mol of o-nitrophenylhydrazine gave the bis(o-nitrophenylhydrazone) 2, oxidation of which with cupric chloride afforded 3,6-anhydro-3-(o-nitrophenylazo)- l -xylo-2-hexulosono-1,4-lactone 2-(o-nitrophenylhydrazone). Controlled reaction of 1 with o-nitrophenylhydrazine gave the 2-(o-nitrophenylhydrazone) 8, which underwent dehydrative acetylation to yield 4-(2-acetoxyethylidene)-4-hydroxy-2,3-dioxobutyro-1,4-lactone 2-(o-nitrophenylhydrazone). The reaction of 8 with phenyl- and benzoyl-hydrazine afforded the mixed bis(hydrazones) 10 and 11. Oxidative cyclisation of 10 with cupric chloride gave 3,6-anhydro-3-phenylazo- l -xylo-2-hexulosono-1,4-lactone 2-(o-nitrophenylhydrazone). The reaction of 8 with methylhydrazine yielded the expected mixed bis(hydrazone) 19, which was dehydrated during the acetylation and gave 4-(2-acetoxyethylidene)-4-hydroxy-2,3-dioxobutyro-1,4-lactone 3-(N-acetylmethylhydrazone) 2-(o-nitrophenylhydrazone). The condensation of 8 with hydroxylamine and semicarbazide was also studied.

An unusual equilibrium between a cyclopropylcarbonyl compound and a 2,3-dihydrofurane derivative

Abstract The equilibrium data of the thermal interconversion between a cyclopropylcarbonyl derivative with trispiro structure and a dihydrofuro[2,3-c]pyrazole have been examined.

Synthese furanoider Zuckeraminos¨auren ausgehend von fermentativ gewonnener 2-Oxo-D-gluconsäure / Synthesis of Furanoid Sugar Amino Acids Starting from Fermentatively Produced 2-Oxo-D-gluconic Acid

2-Oxo-D-gluconic acid obtained by fermentation of D-glucose was used as starting material for syntheses of amino acids. We trapped the carbohydrate in its furanoid configuration and synthesized an α- and an ω-amino acid. After deprotection of the hydroxyl groups the latter did not isomerize to the substituted piperidine (aza-sugar) as expected, but remained in the furanose form. The starting structure 2 was proven by crystal structure analysis. The conformational identification of the other substances was done by NMR measurements following known rules for furanoses.