D-GULONIC ACID, y-LACTONE

N-methyl-l,2-diphenylethylamine, 34, 64 tetraphenylarsonium chloride hydrochloride, 30, 97 Guanidine, 32, 96 Guanidine hydrochloride, 32, 45 Guanylthiourea, 35, 69 D-GuLONIC ACID, y-LACTONE, 36, 38... 

The y-lactone of D-gulonic acid was prepared by way of a cyanohydrin derived from an aldopentose. 

Starting from D-gulonic-y-lactone the salt was formed and a 0.5 M solution converted to D-Jcy/o-hex-2-ulosonate sodium salt monohydrate in the same manner as described for the preparation of sodium D-araZ>/ o-hex-2-ulosonate. Part of it was converted to methyl-D-xy/o-hex-2-ulosonate, and this further to D-/Areo-hex-2-enono-1,4-lactone (D-ascorbic acid) as described (72). The H and C-NMR spectra in H20 are identical to those of an authentic sample of L-ascorbic acid. 

The nitrone 266 bearing a D-gulono-y-lactone auxiliary directs addition of methylmagnesium bromide as a key step in synthesis of (/7)-zilegton (Scheme 54). The gulonic-acid derived auxiliary 267 has been described as an improvement on a previously reported carbohydrate oxazolidinone auxilary (see Chapter 10)... 

The basic biologically active compound is ascorbic acid. Of the four possible stereoisomers (asymmetric carbons C-4 and C-5), the activity of vitamin C is seen only in L-ascorbic acid h-threo-hex-2-enonic acid 1,4-lactone formerly called ceritaminic acid, 2-keto-L-gulonic acid, L-xy/o-hex-2-ulosonic acid and later L-xylo-ascorbic acid). The D-isomer of ascorbic acid (n-xy/o-ascorbic acid) and the second pair of enantiomers, known as l- and d-isoascorbic acids (5-106 to 5-109), do not show vitamin C activity. Previously, these acids, which are y-lactones of l- and v-erythro-hex-2-enonic acids, were known as l- and o-erythorbic acids or L- and D-arabino-ascorbic acids. 

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