The synthesis of higher carbon sugars: a study on the rearrangement of higher sugar allylic alcohols (original) (raw)
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Application of the triisobutylaluminum-promoted reductive rearrangement to sucrose-5-enes
Israel Journal of Chemistry, 2000
Carbohydrate-based vinyl acetals (5-hex-enopyranosides) undergo reductive rearrangement with triisobutylaluminum (TIBAL) to afford highly functionalized cyclohexanes in which both the aglycon and anomeric stereochemistry are retained. Here, we report the first application of this process to the rearrangement of hex-5-enopyranosides of sucrose in which the interglycosidic oxygen atom of the vinyl acetal system links the anomeric centers of both monosaccharide units. The sucrose-derived 5-hex-enopyranoside 1 undergoes smooth reductive rearrangement with TIBAL to afford the (1→2′) ether-linked pseudo-disaccharide 2 in 34% yield. The rearrangement is accompanied by some loss of stereochemical integrity at C-2′ due to a competitive exo-cleavage of the interglycosidic (O-C2′) bond, hence diastereomers at C-2′ are also obtained in 12% yield. The 4-O-allyl-protected sucrose-5-ene 3 is similarly transformed into the corresponding (1→2′) ether-linked pseudo-disaccharide 4, illustrating the compatibility of the allyl group with the TIBAL reaction conditions.
The Journal of organic chemistry, 2007
A chemoenzymatic synthesis of deoxy sugar esters is described. The synthesis is based on the O-alkylation of carboxylic acid with 2-bromo-5-acetoxypentanal. The method allows treatment of hydroxy carboxylic acids without protection of alcoholic hydroxyl groups. Several stereoisomeric deoxy sugar esters were resolved (up to ee or de > 98%) using a lipase-catalyzed acetylation of hemiacetals that in certain cases afforded deoxy sugar derivatives in the form of aldehydes. The stereochemistry of the reactions was determined by the NMR spectra of mandelic acid derivatives.
Article Syntheses of Enantiopure Aliphatic Secondary Alcohols and
2012
The lipase B from Candida antarctica (Novozym 435 ® , CALB) efficiently catalyzed the kinetic resolution of some aliphatic secondary alcohols: (±)-4-methylpentan-2-ol (1), (±)-5-methylhexan-2-ol (3), (±)-octan-2-ol (4), (±)-heptan-3-ol (5) and (±)-oct-1en-3-ol (6). The lipase showed excellent enantioselectivities in the transesterifications of racemic aliphatic secondary alcohols producing the enantiopure alcohols (>99% ee) and acetates (>99% ee) with good yields. Kinetic resolution of rac-alcohols was successfully achieved with CALB lipase using simple conditions, vinyl acetate as acylating agent, and hexane as non-polar solvent.
Rare sugars and sugar-based synthons by chemo-enzymatic synthesis
Enzyme and Microbial Technology, 2000
The unique catalytic potential of the fungal enzyme pyranose oxidase was demonstrated by preparative conversions of a variety of carbohydrates, and by extensive chemical characterization of the reaction products with NMR spectroscopy. The studies revealed that POx not only oxidizes most substrates very efficiently but also that POx possesses a glycosyl-transfer potential, producing disaccharides from -glycosides of higher alcohols. Although most substrates are oxidized by POx at the C-2 position, several substrates are converted into the 3-keto-derivatives. On the basis of these products, strategies are developed for the convenient production of sugar-derived synthons, rare sugars and fine chemicals by combining biotechnical and chemical methods.
Stabilised tributylphosphonium ylids Bu 3 PCHvCH(EWG), where EWG is CO 2 Me, CO 2 t Bu or CN, react with protected sugar lactones under mild conditions to give high yields of glycosylidene derivatives (4 and 5) with good Z/E selectivity. X-Ray crystallography shows that in the solid state the tetra-O-benzyl protected (Z)-glucosylideneacetonitrile (Z)-4c adopts a conformation intermediate between a boat and a twist-boat, whereas the isomeric galactose derivative (Z)-5c exists as a distorted chair. NMR data suggest that in solution chair-like conformations are again more favoured for galactosylidene derivatives than for their glucosylidene analogues. Solution phase NMR studies and molecular modelling show that the (E)-double bond geometry disfavours the chair-like geometry of the ring, even in the galactose series; this is consistent with the avoidance of allylic 1,3-strain. Reduction of the glycosylidene double bond to give stereoselective formation of b-C-glycoside derivatives may be achieved by using Et 3 SiH-CF 3 CO 2 H or Et 3 SiH-BF 3 ·Et 2 O. q
Chemische Berichte, 1980
Pyranose-derived 1,2-enol acetates of type 4 readily react with 3-chloroperbenzoic acid in ether to an anomeric mixture of glycos-2-uloses 6, as is demonstrated by the conversions 7 -+ 11/12, 18 + 19/20 and 21 + 22. Structural and configurational assignments were based on NMR-data, on the characterization of hydrogenation products (10 and 23), and on the independent formation of 11, 12, and 22 by Ru04-oxidation of the respective partially acetylated pyranoses 8, 9, and 23. -Acid-catalyzed acetylation converts the glycos-2-uloses into their 2,2-diacetoxy derivatives (13, 24, and 35) with anomerization of 0-isomers, whereas cautious treatment with acetyl chloride/pyridine affords the peracetylated 2,3-dehydropyranoses 15, 17, and 36 with retention of configuration at C-1. Mildly basic conditions initiate the elaboration of the y-pyrone systems (42/43) uia double elimination of acetic acid, the respective intermediates, 3,2-enolones 37a, 37 p, and 38, being readily isolable. The alternate triacetyl-enediolone 41, allegedly40) an intermediate in the conversion 11 ---* 42 could be excluded as an intermediate on the basis of its synthesis from tetraacetyl-glucose by oxidation and elimination of acetic acid (44 + 45 -+ 41).
Tetrahedron Letters, 1987
Sutnmahy -The phollahy hydRox@ ghOUpb 06 a-c-g&cobe and me&@-a-c-gLucobide WeRe bC!kc.ti-veLy eM&~ied by &eating -the dhee bugakb wLth N-a~~kiazo~~ine-Z-fkion~, thu6 &,(0/zding heApetiv@ 6-f-a@-c-g©nanobeA and mtihyL-6-g-acyl-a-P-gkkcopyhanobideb in high y&&l.&. JhA MW h&XtioVI .i~ compatied wtih au/r phevioUb bynthekb 06 I-a-a@-p-c-g~UCOpyhUVLObeA dhom p-c-g4kcobe and intenpheied in tenmb 06 anomekc e66ect. Esters in the 6 position of mono-and disaccharides are generally obtained according to two main methods. The most important one involves the synthesis of selectively protected intermediates followed by esterification of the remaining free hydroxyl with an acyl chloride, and subsequent removal of the protecting groups. 1 As an illustration of the second method, 6-&acyl-a-D-glucopyranoses were obtained by direct reaction of an acyl chloride with unprotected a-glucose 1 in pyridine solution. 233 In the latter case, the 6-monoesters of type 2 were obtained in low yields (IO-30 %), together with 1,6-, 2,6-diesters and 1,2,6-triesters of glucose. Moreover, the purification of the above monoesters was tedious. More recently, JENKINS4 prepared the 6,6'-dipalmitates of trehalose and saccharose in satisfactory yields (55 % and 36 % yields respectively), by treating the corresponding unprotected sugar with triphenylphosphine, diisopropyl azodicarboxylate and palmitic acid in DMF solution, thus applying in the carbohydrate field the MITSONOBU reaction.5 A recent paper6 describing an enzymatic preparation of monoacylated sugars, prompted us to display our new method for the syntheses of 6-g-acyl-Q-glucopyranoses 4 and methyl-6-g-acyl-a-g-glucopyranosides 5, which is more convenient, in matter of yields, reaction time, temperature and molar ratios of the reactants as well. Thus, a solution of m-g-glucose 1 or methyl-a-Q-glucoside 2 (3 equ.) and N-acylthiazolidine-2-thione A7 (1 equ.) in dry pyridine8 was treated with a catalytic amount of NaH and 4-dimethylaminopyridine. The reaction was carried out at room temperature and was followed by TLC. The yellow colour of the acylating agent 2 gradually disappeared within l-2 hours. The mixture was then extrated according to our usual procedure.' The esters 2 were isolated from mercaptothiazoline 5 by column chromatography on silica-gel and then recrystallizated from acetone. The yields of pure monoester varied from 60 to 88,4 % with regards to the acylating reagent 3 (see table). The monoesters 2 were isolated in theaform or as a mixture of a and p anomers after column chromatography and repeated crystallisation for separating them chromatog. (a) 67 -id-63 -id-66 -id-60 -id-61 -id-88. -id-70 -id-m.p. ("C) 133 -135 134 -135 136 -139 46 -49 63 -66 71 -72 78 -80 86 -91 Solvent for recrystall. AcOEt/hexane -id-EtOH Me2C0 -id--id--id--id-(a) silica gel MERCK 60 H ; elution with CH2C12 followed by Me2CO/CH2C12 50 : 50 V/V and then Me2CO The structures of the esters 2 and 2 were determined by elemental analysis, IR and N M R and comparison with published data. 2,399 The ester group was characterized by a very fine absorption band located near 1730 cm -1 in the IR spectrum, that is, at a frequency lower than for the lp-monoesters we previously obtained 9b,lO or than for the la-monoesters. 3 The 'H-NMR spectrum (DMSO-d6) showed a signal centred neara4,9 ppm (Jl 2 = 3.5 Hz) for compounds 4 and 84.6 ppm (Jl,2 = 3 Hz) for esters 5, characteristic of the animeric 1 proton. And as expected, the triplet neara4.5-4.7 ppm typical of the primary 6-hydroxyl did not show up. In deuterated pyridine, the Hl proton of 5 appeared at S 5.08 ppm (Jl 2= 3 Hz) and the anomerit proton of the esters 2 resonated at 6 5.9 ppm (Jl 2 = 3.5 Hz). iut after three hours at room temperature, another signal appeared at S 5.9 ppm [JI 2 = 7.5 Hz) as the result of the anomerisation of the la -OH into lp-OH,which evidences ihat esterification did not take place at the anomeric hydroxyl of glucose. The esters 4 did not anomerize in DMSO-d6, which made it possible to run their 13 C-NMR spectra in this solvent. The spectra of esters 4 and 5 presented signals respectively at S 63.89 ppm and S 63.53 ppm due to the C6 carbons, that is 3811 deshielded by ca. 3 ppm compared to the corresponding signal in the spectra of l-p-esters of gluc0se.l'