Ian D. Spenser

The Biogenetic Anatomy of Vitamin B6 A 13C NMR INVESTIGATION OF THE BIOSYNTHESIS OF PYRIDOXOL IN ESCHERICHIA COLI

It is shown by incorporation experiments with 13C bond-labeled substrates, followed by analysis by means of 13C NMR spectroscopy, that two compounds, 1-deoxy-D-xylulose (12) and 4-hydroxy-L-threonine (13), serve as precursors of pyridoxol (vitamin B6) (1) in Escherichia coli. Together, these two compounds account for the entire C8N skeleton of the vitamin. 1-Deoxy-D-xylulose supplies the intact C5 unit, C-2′,2,3,4,4′ of pyridoxol. 4-Hydroxy-L-threonine undergoes decarboxylation in supplying the intact C3N unit, N-1,C-6,5,5′. Both precursors are ultimately derived from glucose. The C5 unit of pyridoxol that is derived from 1-deoxy-D-xylulose originates by union of a triose phosphate (yielding C-3,4,4′) with pyruvic acid (which decarboxylates to yield C-2′,2). D-Erythroate (11) enters the C3 unit, C-6,5,5′, and is therefore an intermediate on the route from glucose into 4-hydroxy-L-threonine.

Growth response to 4-hydroxy-l-threonine of Escherichia coli mutants blocked in vitamin B6 biosynthesis

Mutants of Escherichia coli (pdx B and pdx C) which are blocked in the biosynthesis of pyridoxol (vitamin B6) showed a growth response to 4‐hydroxy‐l‐threonine. This observation constitutes the first direct evidence in support of the view that 4‐hydroxy‐l‐threonine is implicated in the biosynthesis of vitamin B6. 1‐Aminopropan‐2,3‐diol, the decarboxylation product of 4‐hydroxy‐l‐threonine, does not support the growth of these mutants. Deuterium from deuterium‐labelled 1‐aminopropan‐2,3‐diol was not incorporated into pyridoxol.

Biosynthesis of vitamins B1 and B6 in Escherichia coli: concurrent incorporation of 1-deoxy-D-xylulose into thiamin (B1) and pyridoxol (B6)

It is shown by 13C NMR spectroscopy that, in Escherichia coli mutant WG2, the C-2,-3 bond of [2,3-13C2]-1-deoxy-D-xylulose 2 enters C-4,-5 of the thiazole unit of thiamin (B1) 1 and C-2,-3 of pyridoxol (B6) 3, providing the first direct evidence that the intact C5 chain of 1-deoxy-D-xylulose is incorporated concurrently into each of the two B Vitamins.

2H NMR spectroscopy as a probe of the stereochemistry of enzymic reactions at prochiral centres: diamine oxidase

Abstract In the conversion of cadaverine into Δ1-piperideine, of putrescine into Δ1-pyrroline, and of agmatine into 4-guanidinobutanal, catalyzed by hog kidney diamine oxidase (DAO) (E.C. 1.4.3.6 diamine: oxygen oxidoreductase (deaminating)), the si-H from C-1 of the substrate is removed while the re-H from C-1 of the substrate is maintained at the sp2 C atom of each of the products. DAO catalyzed oxidation of cadaverine takes place without detectable isotope effect, while an intramolecular primary isotope effect ( k H si k H si = 4) is observed in the DAO catalyzed oxidation of putrescine. In conflict with earlier reports, incubation of cadaverine in deuterium oxide in the presence of bacterial l -lysine decarboxylase (E.C. 4.1.1.18) did not lead to entry of deuterium into the α-position of cadaverine. Likewise, l -ornithine decarboxylase (E.C. 4.1.1.17) did not catalyze exchange of the α-H of putrescine, nor did l -arginine decarboxylase (E.C. 4.1.1.19) catalyze such an exchange in agmatine.

Biosynthesis of the piperidine nucleus: The occurrence of two pathways from lysine

Abstract 2- 3 H,6- 14 C- dl -Lysine was administered to the intact rat, to intact bean plants ( Phaseolus vulgaris ) and to excised shoots of Sedum acre . Pipecolic acid (IV), which was isolated from each of these tissues, contained 14 C but was free of tritium. Since incorporation of label from 6- 3 H,6- 14 C- dl -lysine into pipecolic acid had previously been shown 1 to take place specifically and to occur without change in 3 H: 14 C ratio in each of these systems, the evidence is now complete that conversion of lysine (I) into pipecolic acid (IV) proceeds via ϵ-amino-α-ketocaproic acid (II) and Δ 1 -piperideine-2-carboxylic acid (III) and not via α-aminoadipic-δ-semialdehyde (VI) and Δ 1 -piperideine-6-carboxylic acid (V). In S. acre , 2- 3 H,6- 14 C- dl -lysine was incorporated into sedamine (X) without change in 3 H: 14 C ratio. It follows that ϵ-amino-α-ketocaproic acid (II) cannot be an intermediate in the biosynthesis of sedamine from lysine, as had been previously suggested. Specific conversion of 6- 3 H,6- 14 C- dl -lysine into sedamine without change in 3 H: 14 C ratio had been demonstrated earlier. This and other evidence had been interpreted to show that α-aminoadipic-δ-semialdehyde (VI) is not an intermediate on the route from lysine to sedamine and other piperidine alkaloids. An alternative pathway, which invokes neither ϵ-amino-α-ketocaproic acid nor α-aminoadipic-δ-semialdehyde as intermediate, is now suggested.

Biosynthesis of mimosine: Incorporation of serine and of α-aminoadipic acid

Abstract Serine serves as a precursor of the alanyl side-chain of mimosine. Activity from α-aminoadipic acid is incorporated into the γ-pyridone nucleus. Pipecolic acid and 5-hydroxypipecolic acid occur in Mimosa pudica .

Biosynthesis of vitamin B6: incorporation of three-carbon units.

Pyridoxol, one of the forms of vitamin B6, is derived from three glycerol units. One of these is incorporated by way of pyruvate as a two-carbon fragment at the oxidation level of acetaldehyde. The other two glycerol units are incorporated intact, possibly by way of triose phosphate.

Biosynthesis of N-methylpelletierine ☆

Abstract The biosynthesis of N -methylpelletierine (VII) was studied in excised shoots of Sedum sarmentosum . Consistent with classical biogenetic concepts, the piperidine nucleus of the alkaloid is generated from lysine, which is incorporated by way of nonsymmetrical intermediates, very probably ϵ-amino-α-ketocaproic acid and Δ 1 -piperideine-2-carboxylic acid. The propanone side-chain originates from acetate. Direct incorporation into the side-chain of an intact three-carbon unit derived from acetoacetate could not be demonstrated.

Biosynthesis of vitamin B6. Incorporation of glycolaldehyde into pyridoxal

Radioactivity from [14C]glycolaldehyde enters pyridoxal phosphate specifically, and is confined to the two-carbon unit C(5)–C(5′). Glycolaldehyde enters as an intact two-carbon unit, the aldehyde carbon atom supplying C-5, and the carbinol carbon atom C-5′ of the vitamin. These observations are interpreted in terms of the early stages of the biosynthesis of vitamin B6.

An NMR study of the Lythraceae alkaloids

Several Lythraceae alkaloids containing either a trans‐fused (decinine, decodine, decaline) or a cis‐fused (decamine, verticillatine, vertaline) quinolizidine ring system were examined by high‐field NMR spectroscopy. One‐ and two‐dimensional NMR techniques were used in order to assign the 1H and 13C chemical shifts. The selective 1‐D TOCSY experiment was particularly helpful for resolving the 1H signals of the quinolizidine ring of some of the alkaloids. The chemical shift data combined with two‐dimensional NOE experiments differentiated the cis‐ and trans‐quinolizidine rings and provided structural information that correlated well with structures derived from molecular modelling. Copyright