The potential of aspartic acid B-semialdehyde as a starting material for the synthesis of more complex amino acids is illustrated by its conversion to L-2-amino hept 4,6-dienoic acid and 2S,4R,5S-2-amino-4,5,6 trihydroxy hexanoic acid.
Aspartic acid B-semialdehyde (I) is an increasingly important synthetic intermediate.'
The aldehyde function of (1) provides a useful handle for manipulation to more complex structures. We describe here some uses of (1).
OH
We required a convenient synthesis of (1) or alcohol (2) Prom inexpensive precursors. The route from BOC-L-Methionine' appeared attractive; however in our hands proved difficult.' The following procedure was found to work very well. The sulphonium salt of L-Methionine (4) prepared by reaction with CH,Br, after removal of excess CH,Br, was treated with NaHCO, to give an aqueous solution of &-homoserine (51, which was used directly. Protection on nitrogen then evaporation provided the sodium salt which was esterified to give the L-homoserine derivative (6). This alcohol (6) proved unstable to chromatography, cyclising to the lactone (7), therefore was oxidised directly with PCC to the aldehyde (8), Cc]D +14.0° (CHCl,), in 40% yield from (3). Commercially available ' L-homoserine (5) after protection and oxidation gives the aldehyde (8) [a]D +12.3O (CHCl,), in 44% yield. This implies that the conversion (3) to (5) must proceed in at least 90% yield. The transformation (3) to (8) is carried out in 'one pot' and represents a convenient and inexpensive preparation of this aldehyde (8).' A variation of this sequence involves acidification after the N-protection. This leads to the lactone (7), m.p. 125-126.5O (lit.,' 125-127O), [U]D -29.5O (CH,OH) (lit.,' D-enantiomer, +29o, CH,OH), in 75% yield from (3).