l‐Tagatose

Synthesis of l-Hexoses

“…The structure and stereochemistry was proven from synthesizing the corresponding l -allosazone and comparing the two . The last of the eight 2-keto-hexoses to be synthesized was l -tagatose 31 , which was achieved in 1937 via l -galactose 30 , which in the same paper was synthesized from d -galactose 29 by head-to-tail inversion (see section , Scheme ). , …”

“…l -Galactose was obtained from d -galactose by intermediacy of d -galacturonic acid and l -galactonic acid. The isomerization was conducted for 5 h in boiling pyridine, which led to a 5% yield of 31 with 82% 30 being recovered . The equilibrium was probably not reached as Morgenlie and collaborators have shown in a recent paper that addition of aluminum oxide speeds up the isomerization and that a 2:1 ratio of 30 and 31 could be obtained after 2 h. They also showed that l -gulose ( 451 ) is converted to a 5:1 mixture of l -sorbose ( 452 ) and 451 by these conditions.…”

“…91 The last of the eight 2-keto-hexoses to be synthesized was L-tagatose 31, which was achieved in 1937 via Lgalactose 30, which in the same paper was synthesized from Dgalactose 29 by head-to-tail inversion (see section 7.5, Scheme 4). 92,93 The related L-tagato-methylose (6-deoxy-L-tagatose) was synthesized directly from the natural occurring L-fucose and represents the first compound to be prepared from the 6-deoxy-2-keto hexoses. 94 As studies of ascorbinic acid synthesis and its derivatives were the main interest, L-sorbomethylose (6-deoxy-Lsorbose) 34 was a desired key intermediate.…”

Synthesis of vitamin C from pectic substances

“…Prior to the present investigation it was known that salts of galacturonic acid on reduction with either sodium amalgam [4,11] or with hydrogen in the presence of catalysts [12) give salts of L-galactonic' acid. Reduction of calcium galacturonate, sodium calcium galacturonate, or sodium strontium galacturonate, with hydrogen, in thepresence of Raney nickel, gave salts of L-galactonic acid in nearly' quantitative yield.…”

“…According to the hypothetical reactions, furfural is derived from both ascorbic acid and the pentoses through the intermediate production of a pentose 1, 2-enediol, XVII. In the case of the pentoses, the 1, 2-enediol yields reductic acid, presumably by reactions (5b), (8), (9b), (11), (12), (13), and (14). Inasmuch as the 1, 2-enediol appears to be formed from ascorbic acid., as well as from the pentoses, one might expect that a closer study of the reaction of ascorbic acid with aqueous acid would also reveal the formation of small amounts of r eductic acid.…”