Conformational analysis in carbohydrate chemistry. V. * Formation of glycosidic anhydrides from heptoses

STEPHEN JOHN ANGYAL AND TRUNG QUANG TRAN School of Chemistry, University of New South Wales, Kensington, N.S. W . 2033, Australia

Received July 11, 1980

This paper is dedicated to Prof. Raymond U. Lemieux on the occasion of his 60th birthday

STEPHEN JOHN ANGYAL and TRUNG QUANG TRAN. Can. J. Chem. 59,379 (1981). The position of the equilibrium between aldoheptoses and their glycosidic anhydrides depends crucially on the configuration of

the heptose. Depending on that configuration, the 1,6-anhydropyranose, the 1,7-anhydropyranose, or the 1,6-anhydrofuranose is the major product, its proportion varying from 99% to less than I%. The position of the equilibrium is predictable from conforma- tional considerations. 1,7-Anhydrofuranoses have not been encountered. The 1,3-dioxane ring of the 1,7-anhydropyranoses was found to assume a skew form.

STEPHEN JOHN ANGYAL et TRUNG QUANG TRAN. Can. J. Chem. 59,379 (1981).

La position de I'equilibre entre les aldoheptoses et leurs anhydrides glycosidiques depend fondamentalement de la configuration de I'heptose. Dependant de la configuration, le produit majoritaire est soit l'anhydro-1,6 pyrannose, soit l'anhydro-1,7 pyrannose ou soit I'anhydro-1,6 furannose et ses proportions varient de 99% ?i moins de 1%. On peut prCdire la position de I'equilibre i partir des considerations conformationnelles. On n'a pas mis en evidence la presence de I'anhydro-1,7 furannose. On a trouve que le cycle dioxanne des anhydro-1,7 pyrannoses presente une forme decalee.

[Traduit par le journal]

Introduction hydroxyl groups, it is possible now to discuss the Although the 1,6-anhydrides of the aldohexoses conformational analysis of anhydroheptoses by

have been extensively studied and widely used as analogy to that of the anhydrohexoses, and to make synthetic intermediates (2), very little was known predictions about the proportion of the anhy- until recently about the glycosidic anhydrides of droheptoses at equilibrium. Some of these predic- the aldoheptoses. These anhydrides are formed tions have been tested- from, and are in equilibrium with, the parent al- For the aldoheptoses, three different types of doses in boiling aqueous solutions containing a glycosidic anhydrides are significant: the 1,6- and strong acid. In this way, Richtmyer and his co- 1 ,7-anh~dro-~~ranoses and the 1,6-anh~dro- workers obtained the 1 ,6-anhydropyranose (3) furanoses. The 1,7-anhydrofuranoses, which con- from ~ - ~ l ~ c ~ ~ ~ - ~ - i d ~ - h ~ ~ t ~ ~ e , and the 1,6- and tain fused five- and seven-membered rings, would 1,7-anhydropyranoses (4) from ~ - g ~ y c e r o - ~ - g u ~ o - have low stability and have, in fact, not been en- heptose. Recently, Angyal and Beveridge (1) pre- countered in our work. Other types of anhydrides, pared the 1,6-anhydropyranoses of ~ - ~ l y c e ~ ~ - L - such as the 1 ,4-anhydropyranoses (6), would occur

manno-, D-glycero-L-allo-, and D-glycero-L-altro- in heptoses. These anhydrides were found to be pres- There are sixteen possible diastereomeric al- ent in the equilibrium mixtures in much higher pro- doheptoses (counting eachpair of enantiomers only portion than were the 1,6-anhydrides in the equilib- once); we have not investigated all of them. The ria with the respective aldohexoses. ~h~ higher synthesis of some of the aldoheptoses is quite cum- stability of the heptose anhydrides, compared with bersome and it was that them the hexose anhydrides, was attributed (1) to the yield worthwhile information. Thus, the discussion

ring closure occurring through a secondary, rather which ~ O ~ ~ O W S will allow US to predict with confi-

than through a primary, hydroxyl group. dence, even though we were not able to test our ~h~ proportion of 1 ,6-anhydropyranose in prediction, that D-glycero-L-ido-heptose would be

equilibrium with an aldohexose ranges from 0.2% converted to an extent of over 99% into the 1,6- for glucose to 76% for idose (5). These proportions anh~dro~yranose , and that D-glycero-D-gluco- have been explained in terms of nonbonded in- heptose would yield no anhydride in a proportion

teractions (5). With the recognition that the ten- O.l%. dency for ring formation through primary hydroxyl Results and Discussion groups is different from that through secondary 1,6-Anhydropyranoses

The proportions of 1,6-anhydropyranose in 'For part IV, see ref. I . equilibrium with each aldohexose are (5): glucose,

0008-404218 11020379-05$01.00/0 01981 National Research Councll of CanadaIConseil national de recherches du Canada

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380 CAN. J . CHEM. VOL. 59, 1981

0.2; mannose, 0.8; galactose, 0.8; talose, 22.8; al- lose, 2 14; altrose, 65; gulose, 65; and idose, 76%. When the additional hydroxymethyl group in the 1 ,6-anhydroheptoses is exo, the proportion of the anhydride in equilibrium was found to be consid- erably higher (I), namely, 15% for D-glycero-L- manno-heptose, 54% for D-glycero-L-allo-heptose, and 98% for D-glycero-L-altro-heptose. It is rea- sonable to assume that similar increases would occur in going from the other hexoses to the homomorphous D-glycero-L-heptoses (and their L-glycero-D-heptose enantiomers), the anhydrides of which all have exo hydroxymethyl groups. In fact, we found that on equilibration D-glycero-L- gluco-heptose gave 7.5%, D-glycero-L-galacto- heptose 18%, and D-glycero-L-talo-heptose 31% of the 1,6-anhydropyranose. The structures of these anhydrides were not proven because we had in- sufficient material for their isolation but, by anal- ogy with the other heptoses, it is very likely that they are 1,6-anhydropyranoses. The other anhy- drides of these heptoses would have very un- favourable interactions. The remaining heptoses of this group, D-glycero-L-gulo- and D-glycero-L- ido-heptose, were not available but, by analogy with D-glycero-L-altro-heptose, one can confident- ly predict that they would be converted into the 1,6-anhydropyranoses to the extent of at least 98%.

The 1,6-anhydropyranoses of the D-glycero-D- heptoses (and their L-glycero-L-heptose enantio- mers) have the hydroxymethyl group in the endo configuration (1) and are therefore less stable than the homomorphous hexose derivatives. Thus we found that D-glycero-D-gulo-heptose yields only 11%, and D-glycero-D-ido-heptose 35%, of the 1,6-anhydropyranose (compared with 65 and 76% for the hexoses). One would then predict that D-glycero-D-altro-heptose would give the 1,6- anhydride in a proportion similar to that of the gulo compound, and that D-glycero-D-gluco-, -D- manno-, -D-galacto-, and -D-talo-heptose would

yield only traces of the anhydride. In fact, on equilibration of the galacto and talo isomers we found (by glc) only very small amounts (<0.5%) of compounds which could be the 1,6-anhydro- pyranoses. D-glycero-D-allo-Heptose yielded ap- proximately 3% of the 1,danhydride; this is about the proportion one would have predicted by com- parison with allose (14%)). 1,7-Anhydropyranoses

Only one anhydride of this type has been de- scribed, 1 ,7-anhydro-D-glycero-PD-gulo-hepto- pyranose, obtained in about 10% yieldZ from the heptose on equilibration (4). We found that D- glycero-D-ido-heptose gave 40% of the 1,7- anhydride. The ring system contained in these anhydrides (analogous to the bicyclo[3,3, llnonane system) is inherently unstable owing to the interac- tion, in the twin-chair form (2), between the endo hydrogen atoms on C-3 and C-7. The strain in bicyclo[3,3,l]nonane has been estimated (7) to be -42 kJ mol-I. The 1,7-anhydrides appear to be about equal in stability to the 1,6-anhydrides with an endo hydroxymethyl group; judging by models, the configuration of C-6 does not appear to affect the stability to any significant extent, except in those cases when 0-4 is equatorial: the 1,7- anhydride of a D-glycero-L-heptose would then have a parallel 1,3-interaction between 0-4 and 0-6.

These considerations indicate that D-glycero- D-altro-heptose (which we did not have) would give about 10% of the 1,7-anhydride, and D-glycero-D- allo-heptose, about 4%. In fact, equilibration of the latter compound produced an anhydride in 4.3% yield; this we believe to be the 1,7-anhydride. The 1,7-anhydride of D-glycero-L-altro-heptose would have a stability similar to that of the D-glycero-D- altro compound but would hardly be detectable in the presence of the overwhelming proportion (98%) of the 1,6-anhydride. None of the other heptoses would yield a substantial proportion of the 1,7- anhydropyranose.

In fact, the other heptoses we investigated did not yield any compound that we could recognize as the 1,7-anhydropyranose. D-glycero-L-allo-Hep- tose gave two minor components (beside the 1,6- anhydropyranose); one of these is probably the 1,7-anhydropyranose.

In order to identify the anhydride obtained from D-glycero-D-ido-heptose as the 1,7-anhydride, we studied its nmr spectrum and, for comparison, also

2Angyal and Dawes (5) reported a much higher conversion (66%) but we were unable to repeat their results. Even after 72 h boiling with 5% sulfuric acid, only 11.4% of the 1,7-anhydride was found to be present, and the amount no longer increased with time.

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ANGYAL AND TRAN 38 1

those of 1,7-anhydro-D-glycero-D-gulo-hepto- pyranose and of the 1,6-anhydrides of these two heptoses. In all of these spectra, only the signal of H-1 could be distinguished, the other signals over- lapping extensively. However, when these com- pounds were acetylated, the signals of H-2, H-3, H-4, and either H-6 or H-7 and H-7' shifted downfield, and all the spectra could be fully analysed. In the spectra of the acetylated 1,6- anhydrides, the signals of H-5 and H-6 were at highest field, showing thereby that C-5 and C-6 do not carry acetoxy groups. On the other hand, in the spectra of the acetylated 1,7-anhydrides, the sig- nals of H-5, H-7, and H-7' were at highest field.

The conformations of these 1,7-anhydrides are of interest. Bicyclo[3,3, llnonane, in the absence of endo substituents which would cause steric in- teraction, is predominantly in the twin-chair form, with the chairs somewhat flattened (8). It has been suggested, however, that in the 1,7-anhydro- pyranoses the interaction between H-3 and H-7 may be sufficiently large to encourage the 1,3- dioxan ring to exist, at least partially, in a boat conformation (9). In fact, the nmr spectra of the acetates clearly show that the anhydride ring is not in the chair form (2): in that form, J,,6, J6,7, and J6,,, would all have values of-3.5 Hz. In the spectrum of tetraacetyl-l,7-anhydro-D-glycero-P-D-gulo- heptose these values are 1.2, 7.1, and 9.0Hz, re- spectively, which seems to indicate that the 1,3- dioxan ring is in the skew form (3). The ido anhydride has somewhat smaller coupling con- stants (1.0, 5.3, 5.1 Hz); there seems to be more of the twin-chair form in equilibrium with the skew form. Accordingly, the pyranose ring is somewhat flattened (J2,3 and J 3 , are less than 10 Hz).

1,6-Anhydrofuranoses No anhydrofuranose derivative of an aldohep-

tose has so far been reported. From the aldo- hexoses, small amounts (0.04-2.5%) of the 1,6- anhydrofuranoses are produced on equilibration in acid solution (5, 6, lo), in addition to the predomi- nant 1,6-anhydropyranoses. The anhydrofur- anoses of talose and altrose occur in the highest proportion (2.5 and 1.6%), followed by those of allose (1.0%) and galactose (0.95%). Since the for- mation of the 1,6-anhydrofuranose from an al- doheptose would involve ring formation through a secondary hydroxyl group, it is predictable that the anhydride will be formed in a considerably higher proportion than it is from the homologous hexose, provided that the additional hydroxymethyl group is exo and therefore its presence does not introduce an unfavourable steric interaction.

Of all the diastereomers, the 1,6-anhydro-

furanose of D-glycero-D-talo-heptose would be the energetically most favourable one: 0-2, 0-3, and C-7 are exo and 0-5 is equatorial. It was found that this heptose gave one anhydride in 11.2% yield. The nmr spectrum of its acetate proved that this is, indeed, the anhydrofuranose (4): J,,, and J 3 , are smaller than 0.5 Hz and J2,3 is 6.7 Hz. The spec- trum is similar to that of the acetate of 1,6- anhydro-a-D-talofuranose (5). The six-membered anhydro-ring is in the chair form (J , , is 10.0 Hz).

The 1,6-anhydrofuranoses of D-glycero-D- galacto- and D-ido-heptose would differ from the preceding anhydride only in having an endo hy- droxyl group on C-2 and C-3, respectively, and would therefore also be energetically favourable. D-glycero-D-galacto-Heptose produced, on equil- ibration, 7.5% of an anhydride, which was shown to be the 1 ,6-anhydrofuranose by the nmr spectrum of its acetate; this is closely similar to the spectrum of the acetate of 1 ,6-anhydro-a-D-galacto-furanose (11). Although D-glycero-D-ido-heptose is con- verted into the two anhydropyranoses in a yield of nearly 75%, glc shows the presence of another anhydride (1.3%) which presumably is the anhy- drofuranose.

In the D-glycero-L-heptose series, the 1,6- anhydrofuranoses of the gluco, allo, and altro configuration have the most favourable structures (C-7 exo and no, or only one, endo hydroxyl group). In the equilibrium mixtures formed from the gluco and a110 isomers, glc shows the presence of an anhydride in a proportion higher than that of the anhydrofuranose of glucose and allose, respec- tively; these we presume to be the 1,6- anhydrofuranoses though we have not isolated them. Since D-glycero-L-altro-heptose is converted to the 1,6-anhydropyranose to the extent of 98%, the anhydrofuranose was not detected. Additional small peaks are also seen in the glc curves of the equilibrium mixtures from D-glycero-L-galacto- and D-glycero-L-talo-heptoses. These are also be- lieved to represent anhydrofuranoses; although they would have endo hydroxymethyl groups, ring closure through a secondary hydroxyl group would compensate for this steric effect; the proportion of 1,6-anhydrofuranose is about the same as that formed from the homologous hexoses. From D- glycero-L-talo-heptose, yet another anhydride appears to be produced; since the 1,7- anhydropyranose would be energetically un- favourable, we cannot guess its structure.

Chaby and Szabo (12) distinguished the 1,6- and 1,7-anhydroheptopyranoses from each other by the mass spectra of their acetates. The spectra show the same peaks but in different proportions. We recorded the mass spectra of the acetates of the two

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CAN. J . CHEM. VOL. 59, 1981

TABLE 1. Anhydrides (%)formed by acid-catalysed equilibration of aldohexoses in aqueous solution

(<O.I)* (<0.2) Trace Trace

2.9t (10) 10.8 33.5

(-1 (-1

Trace -

4.3t (10) 11.4 39

'NOTE : figures in parentheses are estimates based on analogy. tThe structure of thiscompound has not been unequivocally determine $Reference 1.

1,6-anhydrofuranoses and again found the same peaks in proportions somewhat similar to those in the spectra of the 1,7-anhydrides. The proportions were not the same in the spectra of the galacto and the talo isomer. In view of these results we are disinclined to rely on mass spectra for the determi- nation of the structures of the anhydroheptoses.

The results obtained are summarized in Table 1. For those heptoses which we did not investigate, we estimated the proportion of the anhydrides in equilibrium by analogy with the homologous hexoses and the other heptoses; these estimates are shown in parentheses. Those components whose structures we have not determined are also indi- cated.

Experimental General

Solvents were evaporated under diminished pressure in ro- tary evaporators. All solvents used for chromatography were distilled. "Light petroleum" refers to the fraction boiling be- tween 60 and 80°C; "ethanol" refers to 95% ethanol; mixed solvents were prepared on a vlv basis.

Column chromatography was performed on Merck Silica Gel H (Type 60). Gas-liquid chromatography (glc) was carried out with a custom-built instrument, using nitrogen as carrier gas with a flow-rate of 60-80 mL per min, and a hydrogen flame- ionization detector. The 1.5 m coiled glass column was filled with 3% SP-2401 on Chromosorb W (AW-DMCS) and was kept at 210 or 215°C. Peaks were cut out and weighed; it was assumed that all compounds gave equal detector responses. The com- pounds were analysed by glc as their acetates. Most reaction mixtures showed small amounts of very volatile compounds (R, < 1 min) which could be dianhydrides or decomposition products. The pure heptoses gave up to four peaks after acety- lation: those of the two pyranoses and of the two furanoses.

Thin-layer chromatograms (tlc) were run on Merck Silica Gel G (Type 60), supported on microscope slides, without activa- tion. The compounds were detected by spraying with 20% sul- furic acid in ethanol and then heating on a hot-plate.

Proton magnetic resonance spectra were recorded with JEOL JNM-4H-100 and JNM-FX-100 spectrometers. The spectra de- scribed here were run in deuteriated benzene, using Me4Si as internal standard; most of the spectra were also run in deuteriochloroform but those spectra could not be fully analysed. Mass spectra were recorded with an AEI MS-12 spectrometer by electron impact at 70 eV from a direct insertion probe at 25'C and a source temperature of 230°C. Optical rota-

tions were determined with a Bendix NPL Automatic Polarimeter 143C, equipped with a JANUS digital readout, in a 2 cm cell. Microanalyses were carried out by Mr. J. Sussman in the School's microanalytical laboratory.

Establishment of Equilibria A solution containing the heptose in 5% aqueous sulfuric acid

(20 parts) was heated on a steam-bath for 48 h. Samples removed from time to time, and analysed by glc after acetylation, showed that in every case equilibrium had been reached by that time. The acid was removed by stirring with Amberlite IRA 400 resin in the hydrogen carbonate form until the solution was neutral. Evaporation gave a syrup. In those cases where a large propor- tion of the heptose remained unchanged, some of it was recov- ered by crystallization at this stage. The mixture was then treated with acetic anhydride-pyridine (I: 1) on asteam-bath for 2 h, evaporated, the residue dissolved in chloroform, and washed first with M sulfuric acid, then with saturated sodium hydrogencarbonate solution. After evaporation, the residue was chromatographed on a column of silica gel; the acetates of the anhydrides emerged before those of the heptoses. Some of the acetates crystallized; those that did not, were distilled at a pressure of 0.2-0.3 Torr.

Equilibration of D-glycero-L-gluco-Heptose (13) The glc peaks (215°C): 0.7% (R, 2.1 min), 8.5% 1,6-

anhydropyranose (2.7 min), 51% P-pyranose (6.0 min), and 40% a-pyranose (7.2 min).

Equilibration of D-glycero-L-galacto-Heptose (14) The glc peaks (215°C): 0.6% (2.2min), 18% 1,6-

anhydropyranose (3.2 min), 40% P-pyranose (6.7 min), 13.6% furanose (?) (7.5 min), and 29% a-pyranose (8.3 min).

Equilibration of D-glycero-L-talo-Heptose (14) The glc peaks (210°C): 2.8% (3.5 min), 2.5% (4.2 min), 31%

1,6-anhydropyranose (5.1 min), 37% heptose (15.0 min), and 26% heptose (17.8 min). The substance appearing at 4.2 min is formed more slowly than the other products; after 24h it amounts to only 1.4%.

Equilibration of D-glycero-D-gulo-Heptose (15) The glc peaks (210°C): 11.4% 1,7-anhydropyranose (4.8 min),

10.8% 1,6-anhydropyranose (6.2 min), and four heptose peaks: 68.5% (12.6 min), 2.5% (17 min), 3.6% (19.5 min), 3.2% (22.5 min). The 1,7-anhydride is formed at a slower rate than the 1,6-anhydride; after 24 h the composition was 5.0,9.0,73.9,2.1, 4.6, and 5.4%, respectively.

Column chromatography with ether - petroleum ether (l:3) as eluant gave, in fractions 7-12, 2,3,4,6-tetra-0-acetyl-1,7- anhydro-D-glycero-P-D-gulo-heptopyranose, [aIDz2 +48.5J0 (C 1.43, CHCI,); nmr 6: 1.44, 1.62, 1.71, 1.91 (Ac), 3.59(dd, H-7', J6 ,72=9 .0 , J7 ,7 ,= -10.8),3.71(H-7,J6,7=7.1),4.59(dd,H-5, 54.5 = 6.3, J 5 . 6 = 1.2). 5.06(d, H-I , J1 .2= 1.8),5.14(ddd, H-61,

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ANGYAL A N D TRAN 383

5.57 (dd, H-2, J2,, = 3.8), 5.59 (dd, H-4, J3,4 = 10.3), 5.85 (dd, H-3). Anal. calcd. for C15H20010: C 50.00, H 5.59; found: C 50.23, H 5.56.

Fractions 21-39 gave 2,3,4,7-tetra-0-acetyl-1,6-anhydro-D- glycero-P-D-gulo-heptopyranose, +20.1° (C 1.61, CHCI,); nmr 6: 1.59 (Ac), 1.64 (Ac), 1.68 (~Ac) , 3.99 (quin, H-6), 4.27 (t, H-5, J4.5 = J5,, = 4.l), 4.35 (dd, H-7', J6,7' = 4.2, J7,7, = - 12), 4.49(dd, H-7, J6,,= 7.5),5.30(d,H-1, J,,,= 2.3), 5.44(dd, H-2, J 2 ,= 5.0), 5.52 (dd, H-4, J,., = 9.6), 5.84(dd, H-3). Anal. calcd. for C15H20010: C 50.00, H 5.59; found: C 49.90, H 5.37.

Equilibration of D-glycero-D-ido-Heptose (15) The glc peaks (210°C): 39% 1,7-anhydropyranose (2.5 min),

33.5% 1,6-anhydropyranose (2.8 rnin), 1.3% anhydrofuranose (?) (4.4 rnin), and four peaks ofthe heptose: 3.2% (7.7 rnin), 4.2% (10.6 rnin), 15.4(11.8 rnin), 3.4%(14.5 rnin).

Column chromatography with ethyl acetate - light petroleum (1:4) as eluant gave, in fractions 28-40, 2,3,4,6-tetra-0-acetyl- 1,7-anhydro-D-glycereP-D-ido-heptopyranose which crystal- lized from benzene - light petroleum as needles, mp 74-76°C; [a],,, -34.S0(c 1.48, CHCI,); nmr6: 1.51, 1.66, 1.73, 1.85 (Ac), 3.60(dd, H-7',J6,72= 5.1, J7.7, = -12.7), 3.80(dd, H-7,J6,7= 5.3), 4.36 (broad d, H-5), 4.93 (dt, H-6, J5,, = 1.0), 5.11 (dd, H-2, J,,, = 3.7, J2,, = 9.0), 5.28 (broad d, H-1), 5.32 (dd, H-4, J,,, = 9.5, J4,, = 6.6), 5.99 (t, H-3). There appears to be long-range coupling between H-l and H-5. Anal. calcd. for C15H20010: C 50.00, H 5.59; found: C 50.92, H 5.80.

Fractions 46-56 gave 2,3,4,7-tetra-0-acetyl-1,6-anhydro-D- glycero-P-D-ido-heptopyranose, [aIDz3 -53" (c 1.15, CHCI,); ' nmr 6: 1.59, 1.60, 1.65, 1.70(Ac), 4.03 (quin, H-6), 4.14 (t, H-5, J5,,= 4.21, 4.34(dd, H-7', J6,7'= 6.2, J7,7r= -12.1),4.50(dd, H-7, J,,, = 7.6), 5.05 (d, H-2, J,,, = 1.7, J,,, = 8.0), 5.28 (ddd, H-4, J3,4 = 9.0, J4.5 = 4.5, J4., = l . l) , 5.43 (d, H-1), 5.87 (dd, H-3). Anal. calcd. for C15H20010: C 50.00, H 5.59; found: C 50.79, H 5.84.

Equilibration of D-glycero-D-allo-Heptose (16) The glc peaks (215°C): 4.3% 1,7-anhydropyranose (?)

(3.0min), 2.9% 1,6-anhydropyranose (?) (3.8 rnin), 71.6% P- pyranose (8.3 min), and three other forms of the heptose: 10.8% (10.5 rnin), 4.2%(11.6 rnin), 6.1%(13.5 rnin).

Equilibration of D-glycero-D-galacto-Heptose (17) The glc peaks (210°C): 8.5% 1,danhydrofuranose (6.8 min),

0.5% (9.3 min), 0.5% (10.1 rnin), 47.5% heptose (16.5 min) and 43.5% (23.3 rnin). Column chromatography over silica gel (10 parts) with ether - petroleum ether (l:2) (10 mL fractions) gave, in fractions 14-21, 2,3,5,7-tetra-0-acetyl-1,danhydro-D- glycerep-D-galacto-heptofuranose, +151.3" (c 1.25, CHCI,); nmr 6: 1.51 (Ac), 1.62 (Ac), 1.82 (~Ac) , 4.0-4.35 (m, 3H, H-6, 7, 77, 4.67 (d, H-4, J4,, = 4.6), 5.09 (dd, H-5, J5,, = 9.11, 5.18 (ddd, H-2, J1,Z = 4.8, J2,, = 2.5. J2,5 = 0.6), 5.40 (d, H-3, J,,, = O), 5.63 (d, H-1). Mass spectrum mle (relative abun- dance): 43 (100), 81 (8), 82(8), 110(10), 111 ( l l ) , 115 (IS), 153 (a), 157 (11). Anal. calcd. for C,5H20010: C 50.00, H 5.59; found: C 50.47, H 5.64.

trace(7.8 rnin), and three peaks ofthe heptose: 22.5% (1 1.6 min), 58% (15.5 rnin), 7.5% (17.7 rnin). Column chromatography, as above, gave in fractions 11-18, 2,3,5,7-tetra-0-acetyl-D- glycero-a-D-talo-heptofuranose, [a],,, + 106.5' (c 1.3, CHCls); nmr6: 1.60, 1.64, 1.71, 1.81 (Ac), 3.29(dt, H-6, J5,,= 10.0, J,,, +J6,7~=7.0),4.10(dd,H-7',J7,7~=-12.1),4.11(dd,H-7),4.76 (d,H-4, J4,5=4.6),5.04(dd,H-5),5.33(d,H-3, J2,3=6.7, J3.4= < 0.5), 5.39 (s, H-1, J,,, = O), 5.43 (d, H-2). Mass spectrum mle (relative abundance): 43 (100), 63 (6), 81 (81, 82 (71, 97 (6), 110 (IS), 111 (12), 115 (20), 153 (8), 157 (11). Anal. calcd. for C15H20010: C 50.00, H 5.59; found: C 51.38, H 5.70.

Acknowledgments This work was supported by a grant from the

Australian Research Grants Committee. The au- thors are grateful to Mrs. Donna Range for carrying out some of the preliminary experiments and to Dr. V. Bilik (Bratislava) for a gift of samples of D- glycero-L-galacto- and D-glycero-L-talo-heptoses.

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The glc peaks (210°C): 12.2% 1,danhydrofuranose (5.7 min), 4662 (195 1).

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