D-Erythro isomer

Of the four possible 5-deoxy-pent-4-enofuranoses, the D-erythro-isomer was of interest as a potential source of derivatives of L-lyxofuranose. For this purpose, a vinyl ether having the D-en/ hro-configuration has been prepared from derivatives of D-ribose. Condensation of D-ribose with acetone in the presence of methanol, cupric sulfate and sulfuric acid at 30°C., as described by Levene and Stiller(30) afforded a sirupy product consisting mainly of methyl 2,3-O-isopropylidene-D-ribofuranose (40). Treatment of a pyridine solution of the sirup with tosyl chloride... 

The structure of 3-deoxy-D-erythro isomer, from the formation of osazones, of 5-(hydroxymethyl)-2-furaldehyde with acids, and of metasac-charinic acids with alkali. ... 

Acyclic Alditols. - Brimacombe s group have published full details of their work on the stereoselective synthesis of higher sugars, some of which is covered in Chapter 2 other papers describe the Sharpless oxidation of the octose derivative (1) to give the oxiran (2), and hence the D-erythro isomer (3), osmylation... 

Reaction of 2,3-G-isopropylidene-D-glyceraldehyde with methyl diazoacetate gives predominantly (ca. 5 1) the D-erythro-isom T (3) (Scheme 1), convertible on hydrogenolysis to lactone (4).5 The same product (4) could also be obtained via the epoxyamide (5), which was produced in a 6 1 predominance over the alternative tran5-epoxide when isopropylidene glyceraldehyde was treated with a sulphur ylid (Scheme 1). A full account... 

All four stereoisomers of 4-amino-(2-hydroxymethyl) tetrahydro-furan 4-carboxylic acid (a 2-C-hydroxymethyl pentonic acid derivative) (25) have been synthesized from D-glucose or D-ribose derivatives as outlined in Scheme 9, the threo-isomers spontaneously forming 6-lactones the 2S,4S (D-erythro) isomer was then shown to be the one previously detected in an acid hydrolysate of di abeti c urine. ... 

The V-threo and D-erythro isomers 198 and 199 (which was obtained as the corresponding 7-lactones) were obtained from V-ribono-1,4-lactone with a key step in each case being a stereospecific reduction of an intermediate butenolide." ... 

The stereochemical assignment is based on the comparison of the product with the pure cis and trans isomers (128 and 129) of the enamine prepared by the base-catalyzed elimination of the mesitoate esters of the d/-erythro-2-(4-morpholino)-l,2-diphenylethanol (130) and the <7/-threo-2-(4-morpho-lino)-l,2-diphenylethanol (131). 

Hydrogenation of l-0-acetyl-2,4,6-tri-0-benzoyl-2,3-didehydro-3-deoxy-a-D-erythro-hexose (30) gave a crystalline l-0-acetyl-2,4,6-tri-0-benzoyl-3-deoxyhexose in 60% yield, which on de-esterification with methoxide in methanol afforded 3-deoxy- -D-nfeo-hexose (22). It was not possible to hydrogenate the / isomer under the conditions used for the a form, presumably because the large trans-related C-l and C-4 ester groupings prevent the necessary contact with the catalyst. 

It was noted (23) that the NMR spectrum of compound 32 was identical with that published (34) for the third product (assigned structure 29) isolated from the reaction of tetra-O-acetyl-2-hydroxy-D-glucal with acetic anhydride and zinc chloride. The identity of the compounds was fully established and a revised structure proposed for this third product. In the presence of zinc chloride, therefore, epimerization can occur at an allylic site and the quasi-equatorial C-4 acetoxy group in the erythro isomers 27 and 28 can assume the favored quasi-axial orientation (24). 

Under basic conditions the D-erythro-L-gluco-octonate 88a underwent racemization at C-2 and anomerization at C-3 to give a mixture of four isomeric products. The configurations at C-2 and C-3 of these isomers were established by chemical and physical methods (82). Furthermore, alcohols and thiols, in the presence of a base, attack the double bond of the oct-2-en-onates (87b) affording isomeric oct-3-ulofuranosidonates. 

Methylphenidate possesses two asymmetric carbon moieties, giving rise to four optical isomers d-threo, /-threo, d-erythro, and /-erythro (Patrick et ah, 1987). There is stereoselectivity in receptor site binding and its relationship to response. The standard preparation is comprised of the threo racemate as it appears to be the central nervous system (CNS) active form (Patrick et ah, 1987 Hubbard et ah, 1989). In addition, in rats, the d-methylphenidate isomer shows greater reuptake inhibition of DA and NE than the /-isomer (Patrick et ah, 1987). D-Methylphenidate is now available under the brand name Focalin. 

The reaction of alkyl dihalogenoacetate magnesium enolates with 2,3-isopropylidene-D-glyceraldehyde affords the expected /3-hydroxy-a-dihalogenoesters . The erythro isomer is obtained with isopropyl dichloroacetate magnesium enolate. This result is in agreement with theoretical models. 2-Deoxy-pentono-1,4-lactones are obtained after removal of the halogen atom by either Raney nickel or tributyltin hydride reduction (equation 89). 

Treatment of methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-epimino-a-D-allopyranoside with nitrous acid gave methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-erythro-hex-2-enopyranoside in high yield (81%). The manno isomer likewise gave the same alkene, in 78% yield. The first step in these reactions is the formation of the unstable, yellow IV-nitrosoepimines, the alio isomer being isolated, and crystallized at —20° it was characterized by u.v. and i.r. measurements and by elemental analysis, and could be stored at —20° for a few days.213... 

Brenner et al.333 studied the isomerization of ascorbic acids. Epimerization at C-4 occurs in boiling 50% aqueous methanol containing potassium hydroxide, and an approximately equal mixture of epimers was obtained after 16-24 h. The rare l-erythro- and d-threo isomers of ascorbic acid were isolated as solids by fractional recrystallization of epimerized mixtures... 

Both biopterin (30) and neopterin (31) belong to the family of naturally occurring 6-hydroxypropylpterin and are isolated as major pterins from almost all higher animals. Due to the existence of 2 chiral centers on the propyl side chain, 4 diastereomers are possible in biopterin and neopterin, and isomers 32-37 are found and considered to be minor or exceptional pterins. The absolute configurations of biopterin and neopterin are R,2 S and l S,2 R, respectively, and expedient notations of L-erytho, for biopterin, and d-erythro, for neopterin, have frequently been used. Following these notations, the di-... 

The -)-erythro-isomer of 2,3-dihydroxy-3-methylpentanoic acid (73) has been synthesized by Crout and Whitehouse, and shown to be identical with the naturally occurring (-)-acid obtained from strigosine.45 trans-Hydroxylation of E-3-methylpent-2-enoic acid with tungstic oxide-hydrogen peroxide gave the ( )-erythro-acid, which was resolved as the quinine salts. The absolute configuration of the (-)-erythro-ac d (73) was determined by degradation (Scheme 4). Methylation,... 

Reduction of a sugar epoxide with lithium aluminum hydride also gives a mixture of deoxy sugars in which one isomer may preponderate. This method has been successfully used22 to synthesize a derivative (5) convertible into 2-deoxy-D-erythro-pentose-2(S)-d. 

A stereospecific reduction of a pseudoglycal has been used to prepare the same isomer.23 Reduction of methyl 4,6-0-benzylidene-2,3-dideoxy-/3-D-erythro-hex-2-enopyranoside (6) with lithium aluminum deuteride led to the stereospecific synthesis of 4,6-0-benzylidene-3-deoxy-D-glucal-3(S)-d (7), which, after oxidation with osmium tetra-oxide-periodate followed by debenzylidenation, gave 2-deoxy-D-erythro-Tpentose-2(S)-d (2-deoxy-2-deuterio-D-arabinose) (8). Reduc-... 

Decarboxylation must lead to incorporation of a proton from the solvent. The oxidative decarboxylation of 6-O-phosphono-D-gluconate gives D-erythro-pentulose-1 (S)-t 5-phosphate (with inversion of configuration).45 The R-isomer can be obtained46 from D-ribose 5-phosphate by using D-ribose 5-phosphate ketol isomerase (E.C. 5.3.1.6). 

FDP A was employed in a study of pancratistatin analogs to catalyze the formation of the D-threo stereochemistry (Scheme 5.24). When rhamnulose 1-phosphate aldolase (Rha 1-PA) was used the L-threo stereoisomer was obtained with excellent selectivity. Thus these two enzymes allow the stereoselective synthesis of the two threo-stereoisomers [44]. They were also utilised successfully for the synthesis of different diastereoisomers of sialyl Lewis X mimetics as se-lectin inhibitors. Not only the two threo-selective aldolases RAMA and Rha 1-PA, but also the D-erythro-selective Fuc 1-PA was employed. In this way it was possible to synthesise three of the four diastereoisomers enantioselectively (Scheme 5.25). The L-erythro stereochemistry as the only remaining diastereo-isomer was not prepared [45]. This is because the aldolase that might catalyze its formation, TDP A, is not very stereoselective and therefore often yields mixtures of diastereoisomers. 

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