Chemoenzymatic synthesis of the epimeric 6C-methyl-D-mannoses from toluene

Abstract

The title compounds 1 and 2, which are effective and specific inhibitors of phosphohexomutases, have been prepared in enantiomerically pure form from toluene. The initial step of the reaction sequence involves enzymatic cis-1,2-dihydroxylation of toluene by E. coli JM109 (pDTG601) to give the cis-1,2-dihydrocatechol 3. The latter compound is then converted, [italic v]ia a series of chemical oxidation and reduction steps, into compounds 1 and 2. The X-ray crystal structures of the bis-acetonide derivatives 11, 13 and 14 have been determined.

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A major focus within the burgeoning field of glycobiology is the identification of specific inhibitors of enzymes involved in carbohydrate metabolic pathways and the subsequent development of a detailed mechanistic understanding of the modes of action of these inhibitors.¹ Such studies could provide useful insights into various genetic disease states associated with faulty carbohydrate metabolism.² Recently, Fleet and coworkers have reported³ the synthesis of mannose derivatives 1 and 2 then shown that these compounds are good inhibitors of phosphoglucomutase and phosphomannomutase (PMM). These and earlier observations⁴ by the same group suggest that 6-alkylaldohexose derivatives may prove useful as biochemical tools for probing the function of a wide range of carbohydrate processing enzymes. As a consequence of such possibilities we now describe a new approach to the 6-methylaldohexoses 1 and 2 which employs the cis-1,2-dihydrocatechol 3 as starting material. Compound 3 is an enantiomerically pure compound that is readily obtained in large quantities by microbial cis-1,2-dihydroxylation of toluene.⁵ As such there is the prospect of readily generating ²H-, ¹³C- and/or ¹⁷O-labelled derivatives of 3 and, thence, of the compounds 1 and 2.⁶ Such isotopically labelled derivatives of the title carbohydrates could prove especially useful in probing their interactions with enzymes such as PMM.

The reaction sequence used in producing 6S-6C-methyl-D-mannose (1), which was inspired by Hudlicky's seminal contributions to this general area,⁵ is shown in Scheme 1 and starts with the conversion of diol 3 into the corresponding and well-known⁷ acetonide derivative 4 (95%). Reaction of the last compound with osmium tetroxide, in essentially the same manner as described very recently by Seoane et al.,⁸ afforded a ca. 1:1 mixture of products 5 (33%) and 6 (31%) which could be separated from one another by flash chromatography. The diastereoselectivity associated with the conversion 4 → 5/6 derives from the steric demands associated with the acetonide group of the starting material. Treatment of compound 6 with 2,2-dimethoxypropane in the presence of p-toluenesulfonic acid monohydrate afforded the bis-acetonide 7 (96%) which was subjected to ozonolytic cleavage in methanol–dichloromethane followed by a reductive work-up with dimethyl sulfide.⁹ In this manner an unstable and ca. 3:1 mixture of what is tentatively assigned as the hydroperoxide 8¹⁰ and its corresponding aldehyde was obtained. Reaction of this mixture with sodium borohydride then gave a mixture of diols 9 (10%) and 10 (56%) which could be separated from one another by high-pressure liquid chromatography. Interestingly, when this reduction was effected using lithium borohydride an 8:92 mixture of diols 9 and 10 was obtained, whereas the use of DIBAL-H as reductant gave compound 10 (56%) as the only isolable product of reaction. Selective oxidation of the primary hydroxyl group within diol 10 could be achieved using the sterically demanding oxammonium salt derived from 4-acetamido-TEMPO and sodium hypochlorite,¹¹ and in this way the crystalline lactone 11 was obtained (81%) and its structure determined by single-crystal X-ray analysis (Fig. 1 and Table 1).

Scheme 1 Reagents and conditions: i, Me₂C(OMe)₂, p-TsOH·H2O (10 mol%), −10 °C, 2 h; ii, OsO₄ (cat.), NMMNO (2.0 mol equiv.), Me₂CO–H₂O (1:1 v/v), 60 °C, 0.5 h; iii, O₃ , CH₂Cl₂–MeOH (5: 2 v/v), −78 °C, 2 h then Me₂S (15.0 mol equiv., −78 to 18 °C, 2 h; iv, NaBH₄ (4 mol equiv.), MeOH, 0 °C, 3 h; v, 4-(AcNH)TEMPO (10 mol%), KBr (25 mol%), Bu₄NI (10 mol%), NaOCl (1.34 M aqueous solution, 2.2 mol equiv.), NaHCO₃–brine (buffered to ca. pH 10), 0 °C, 2 h; vi, DIBAL-H (3.0 mol equiv.), −78 °C, 5 min; viii, CF₃CO₂H–H₂O (3:2 v/v), 18 °C, 16 h; vii, Me₂CO, (+)-CSA (20 mol%).

Fig. 1 CS Chem3D Std^TM drawing of compound 11 generated using data derived from an X-ray crystallographic study.

Table 1 Crystallographic data for compounds 11, 13 and 14

11	13	14
Formula	C13H20O6	C13H22O6	C13H20O6
FW	272.3	274.3	272.3
Size/mm	0.28 × 0.04 × 0.26	0.08 × 0.08 × 0.2	0.003 × 0.2 × 0.2
Crystal system	Orthorhombic	Orthorhombic	Orthorhombic
Space group	P212121 (no. 19)	P212121 (no. 19)	P212121 (no. 19)
a/Å	8.4308(4)	6.9393(5)	6.5102(2)
b/Å	10.5457(5)	10.5584(8)	8.9104(4)
c/Å	15.6538(8)	19.7333(8)	23.7859(9)
U/Å^3	1391.8(1)	1445.8(1)	1379.8(1)
Z	4	4	4
D c/g m^−3	1.30	1.26	1.311
T/K	200	200	200
λ/Å	0.71073	0.71073	0.71073
μ/cm^−1	0.1	0.1	0.1
No. of reflections	2291 [I>3.0σ(I)]	1649 [I>3.0σ(I)]	2239 [I>3.0σ(I)]
No. of variables	172	172	172
R	0.038	0.038	0.033
Rw	0.039	0.042	0.036
S	0.95	1.01	1.23
Radiation	Graphite monochromated Mo-Kα in all three cases

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Reduction of compound 11 with DIBAL-H at −78 °C then gave lactol 12 which was immediately deprotected using aqueous trifluoroacetic acid. In this manner the target mannose derivative 1 (99% from 11) was produced and, save for the specific rotation, the spectral data derived from compound 1 matched all of those reported³ previously. Final confirmation of the structure of this target molecule was obtained by single-crystal X-Ray analysis (Table 1) of the derived bis-acetonide 13 (64%) which has also been described previously.³ The discrepancy between the [α]_D value (−10 after 10 min in D₂O) derived from our sample of compound 1 and that reported³ by Fleet et al. (+14.2 after 10 min in D₂O) for the same material is rather difficult to reconcile. This is especially so because the specific rotation observed {[α]_D −2.8 [c 0.50 (after 10 min)]} for our sample of the derived bis-acetonide 13 is in reasonable agreement with the corresponding values {[α]_D +0.1 to −7.7 [c 1.00 in CHCl₃ after 169 h] reported by Fleet et al.³

The synthesis of 6R-6C-methyl-D-mannose (2) was achieved using the reaction sequence shown in Scheme 2 and involved initial oxidation of the diol 9 to the lactone 14 (86%) using the oxammonium salt methodology employed in generating congener 11.

Scheme 2 Reagents and conditions: i, 4-(AcNH)TEMPO (10 mol%), KBr (25 mol%), Bu₄NI (10 mol%), NaOCl (1.34 M aqueous solution, 2.2 mol equiv.), NaHCO₃–brine (buffered to ca. pH 10), 0 °C, 2 h; ii, DIBAL-H (3.0 mol equiv.), −78 °C, 5 min; iii, CF₃CO₂H–H₂O (3:2 v/v), 18 °C, 16 h.

Compound 14, the structure of which was confirmed by single-crystal X-ray analysis (Fig. 2 and Table 1), was then subjected to DIBAL-H-mediated reduction and the resulting lactol 15 was immediately hydrolyzed to the target mannose derivative 2 (99% from 14), using aqueous trifluoroacetic acid. Once again, with the exception of specific rotation {[α]_D −13.8 [italic v]s. a reported³ value of +14.2}, the spectral data derived from this compound matched those obtained previously.

Fig. 2 CS Chem3D Std^TM drawing of compound 14 generated using data derived from an X-ray crystallographic study.

The reaction sequences described above for the preparation of compounds 1 and 2 involve the high-pressure liquid chromatographic separation of precursors 9 and 10. The tedium associated with this separation can be avoided by oxidising the mixture of the latter compounds in the manner described earlier and then subjecting the resulting lactones 11 and 14 to purification by flash chromatography on silica (1:4 ethyl acetate–hexane elution; ΔR_f  = 0.2).

Various analogues of cis-1,2-dihydrocatechol 3 which contain alternate alkyl groups on the six-membered ring are available.⁵ Consequently, the strategy reported here for the preparation of compounds 1 and 2 should be capable of straightforward extension to the synthesis of other 6C-alkyl-D-mannose derivatives.

Experimental

Unless otherwise specified, ¹H and ¹³C NMR spectra were recorded on a Varian Gemini 300 spectrometer using deuterochloroform as solvent. The 500 MHz ¹H NMR spectra and the 150 MHz ¹³C NMR spectrum were obtained on the corresponding Varian Inova spectrometers. Infrared spectra were recorded on either a Perkin-Elmer 683 or 1800 FTIR instrument. Unless otherwise specified, mass spectral analyses were carried out in electron-impact mode and on a VG Micromass 7070F Double-Focussing Spectrometer. Electrospray (ES) mass spectral analyses were conducted on a VG Quattro II instrument. Unless otherwise specified, optical rotations were recorded in chloroform solution at 18–20 °C using a Perkin Elmer 241 polarimeter. Ozonolyses were conducted using a Wallace and Tiernan Ozonator with the oxygen flow rate and power adjusted to ca. 25 l h⁻¹ and 200 V, respectively. Melting points were recorded on a Reichert Hot-Stage microscope and are uncorrected. Thin layer chromatographic analyses were carried out on aluminium-backed, 0.2 mm thick silica gel 60 GF₂₅₄ plates supplied by Merck, while flash chromatographic purifications were conducted according to the method of Still et al.¹² using Merck silica gel 60 (230–400 mesh) as adsorbent. All solvents and common reagents were purified by established procedures.¹³

Synthetic studies

(1S,2S,3S,4S)-3,4-O-Isopropylidene-2-methylcyclohex-5-ene-1,2,3,4-tetraol (5) and (1R,2R,3R,4R)-3,4-O-isopropylidene-5-methylcyclohex-5-ene-1,2,3,4-tetraol (6). Osmium tetroxide (10 drops of a 2.5 wt% solution in tert-butanol) was added dropwise to a magnetically stirred mixture of diene 4⁷ (3.9 g, 23.49 mmol) and N-methylmorpholine-N-oxide (NMMNO, 5.3 g, 43.24 mmol) in acetone (15 ml) and water (15 ml) maintained at 0 °C (ice-bath). The resulting mixture was warmed to 18 °C over ca. 1 h then heated at 60 °C for a further 1 h. The cooled reaction mixture was treated with sodium metabisulfite (50 ml of a 20% w/v aqueous solution) which was then concentrated under reduced pressure. The residue thus obtained was partitioned between dichloromethane (100 ml) and water (100 ml). The separated aqueous phase was extracted with dichloromethane (7 × 100 ml) and the combined organic fractions were then dried (MgSO₄), filtered and concentrated under reduced pressure to afford a tan-coloured oil. Subjection of this material to flash chromatography (40% ethyl acetate–hexane) afforded two fractions, A and B.

Concentration of fraction A (R_f 0.3), afforded diol 5 (1.77 g, 38%) as a pale-yellow oil. The ¹H NMR, ¹³C NMR, MS and IR spectral data obtained on this material were in complete agreement with those reported⁸ by Seoane et al.

Concentration of fraction B (R_f 0.2), afforded diol 6 (1.63 g, 35%) as a pale-yellow oil. The ¹H NMR, ¹³C NMR, MS and IR spectral data obtained on this material were in complete agreement with those reported⁸ by Seoane et al.

(3aS,5aR,8aR,8bS)-2,2,4,7,7-Pentamethyl-3a,5a,8a,8b-tetra hydrobenzo[1,2-d: 3,4-d′]bis[1,3]dioxole (7). A magnetically stirred solution of diol 6 (148 mg, 0.74 mmol) in 2,2-dimethoxypropane (10 ml) was cooled to 0 °C then treated with p-toluenesulfonic acid monohydrate (14 mg, 0.07 mmol). The resulting mixture was allowed to stand at 18 °C for 1 h then treated with triethylamine (1 ml) and concentrated under reduced pressure. The pale-yellow oil thus obtained was dissolved in diethyl ether (10 ml) and the resulting solution washed with water (1 × 10 ml). The separated aqueous phase was extracted with diethyl ether (3 × 10 ml) and the combined organic phases were dried (MgSO₄), filtered and concentrated under reduced pressure to afford compound 7 (170 mg, 96%) as a pale-yellow oil, [α]_D +13.2° (c 1.40), HRMS: found: m/z 225.1128 (M − CH₃)^•+; C₁₃H₂₀O₄ requires 225.1127. ν_max (KBr/cm⁻¹): 2985, 1378, 1369, 1232, 1064; δ_H: 5.44 (br, s, 1H), 4.51 (m, 3H), 4.37 (d, J 4.9 Hz, 1H), 1.82 (s, 3H, 4-CH₃), 1.38 (s, 3H, CH₃), 1.36 (s, 3H, CH₃), 1.35 (s, 3H, CH₃), 1.34 (s, 3H, CH₃); δ_C: 133.8 (C, C-4), 122.1 (CH, C-5), 108.8 (C), 108.7 (C), 73.5 (CH), 73.4 (CH), 73.1 (CH), 71.0 (CH), 27.8 (CH₃), 27.5 (CH₃), 26.3 (2 × CH₃), 19.5 (CH₃); m/z 225 [92%, (M − CH₃)^•+], 125 (100).

7-Deoxy-2,3: 4,5-di-O-isopropylidene-D-glycero-D-manno heptitol (9) and 7-deoxy-2,3: 4,5-di-O-isopropylidene-L-glycero-D-mannoheptitol (10) . A solution of compound 7 (800 mg, 3.33 mmol) in methanol–dichloromethane (7 ml of a 2:5 v/v mixture) was treated, for 2 h at −78 °C, with a stream of ozone (ca. 40% ozone in oxygen). The ensuing solution was purged with oxygen for 10 min then treated with dimethyl sulfide (3.7 ml, 50 mmol) and allowed to warm to 18 °C over ca. 1 h. After 2 h the reaction mixture was concentrated under reduced pressure and the resulting mixture dissolved in methanol (10 ml). The ensuing solution was cooled to 0 °C then sodium borohydride (252 mg, 6.66 mmol) was added in two portions. After 2 h the reaction mixture was acidified (with 2 M aqueous HCl) to ca. pH 4 then diluted with water (60 ml) and extracted with chloroform (8 × 60 ml). The combined organic extracts were dried (MgSO₄), filtered and concentrated under reduced pressure to afford a pale-yellow oil. Subjection of this material to flash chromatography (6:4 ethyl acetate–hexane elution) afforded, after concentration of the appropriate fractions (R_f 0.2), a 15:85 mixture of alcohols 9 and 10. This mixture was subjected to preparative HPLC [Waters μ-Porasil 19 × 300 mm column (part no. 25829), 1:1 ethyl acetate–hexane elution, flow rate 3 ml min⁻¹] and in this manner two fractions, A and B, were obtained.

Concentration of fraction A (R_t 14.84 min) gave compound 10 (516 mg, 56%) as a clear, colourless oil, [α]_D +19.6 (c 1.40), HRMS: found: m/z 261.1339 (M − CH₃)^•+; C₁₃H₂₄O₆ requires 261.1338. ν_max (KBr/cm⁻¹): 3435, 2983, 2936, 1381, 1247, 1215, 1049, 886; δ_H: 4.39 (dd, J 6.5, 2.8, 1H), 4.30 (m, 2H), 4.02 (dd, J 6.7, 2.6, 1H), 3.92 (m, 1H), 3.73 (m, 2H), 3.11 (d, J 3.9, 1H, OH), 2.56 (dd, J 7.5, 5.5, 1H, OH), 1.58 (s, 3H, CH₃), 1.53 (s, 3H, CH₃), 1.39 (s, 6H, 2 × CH₃), 1.25 (d, J 6.6 Hz, 3H, CH₃); δ_C: 109.2(3) (C), 109.1(9) (C), 80.9 (CH), 77.6 (CH), 74.3 (CH), 74.0 (CH), 65.8 (CH), 61.6 (CH₂), 27.0 (CH₃), 26.2 (CH₃), 25.4 (CH₃), 25.2 (CH₃), 20.1 (CH₃); m/z 261 [14%, (M − CH₃)^•+], 187 (15), 173 (22), 59 (100).

Concentration of fraction B (R_t 19.52 min) gave compound 9 (91 mg, 10%) a clear, colourless oil, [α]_D +4.0 (c 0.60), HRMS: found: m/z 261.1340 (M − CH₃)^•+; C₁₃H₂₄O₆ requires 261.1338. ν_max (KBr/cm⁻¹): 3392, 2984, 1382, 1217, 1070; δ_H: 4.54 (dd, J 6.5, 3.9, 1H), 4.30 (m, 2H), 3.98 (br, m, 1H), 3.83 (dd, J 8.9, 5.5, 1H), 3.75 (m, 2H), 2.67 (br, m, 1H, OH), 2.39 (br, d, J 4.3, 1H, OH), 1.54 (s, 3H, CH₃), 1.48 (s, 3H, CH₃), 1.40 (s, 3H, CH₃), 1.37 (s, 3H, CH₃), 1.30 (d, J 6.4 Hz, 3H, 7-CH₃); δ_C: 108.5(9) (C), 108.5(5) (C), 81.1 (CH), 77.6 (CH), 74.9 (CH), 74.4 (CH), 65.6 (CH), 61.4 (CH₂), 27.4 (CH₃), 27.2 (CH₃), 25.6 (CH₃), 25.2 (CH₃), 20.9 (CH₃); m/z 261 [33%, (M − CH₃)^•+], 217 (17), 187 (34), 131 (44), 59 (100).

7-Deoxy-2,3: 4,5-di-O-isopropylidene-L-glycero-D-mannoheptonic acid ε-lactone (11). A magnetically stirred solution of diol 10 (79 mg, 0.29 mmol) and 4-acetamido-TEMPO (6.2 mg, 0.03 mmol) in dichloromethane (5 ml) was treated with sodium bicarbonate (3 ml of a saturated aqueous solution), potassium bromide (8.6 mg, 0.07 mmol) and tetrabutylammonium iodide (10.6 mg, 0.03 mmol). The resulting mixture was cooled to 0 °C then treated, dropwise over 0.75 h, with a solution comprising sodium hypochlorite (470 μl of a 1.34 M aqueous solution, 0.63 mmol), sodium bicarbonate (2 ml of a saturated aqueous solution) and brine (3 ml). After 1 h the reaction mixture was diluted with water (10 ml) and the separated aqueous phase was extracted with dichloromethane (4 × 10 ml). The combined organic layers were washed with brine (1 × 40 ml) and saturated sodium bicarbonate (1 × 40 ml) then dried (MgSO₄), filtered and concentrated under reduced pressure to afford a colourless solid. Subjection of this material to flash chromatography (1:4 ethyl acetate–hexane elution) afforded, after concentration of the appropriate fractions (R_f 0.3), lactone 11 (63 mg, 81%) as colourless crystals, m.p. 132–134 °C, [α]_D −2.7 (c 0.55); HRMS: found: m/z 257.1021 (M − CH₃)^•+; C, 57.1; H, 7.4. C₁₃H₂₀O₆ requires 257.1025; C, 57.3; H, 7.4%. ν_max (KBr/cm⁻¹): 2987, 2939, 1737, 1383, 1255, 1210, 1060, 1015; δ_H: 5.17 (q, J 6.5, 1H), 4.85 (m, 2H), 4.65 (m, 1H), 4.05 (d, J 6.8, 1H), 1.58 (s, 3H, CH₃), 1.49 (s, 3H, CH₃), 1.37 (s, 6H, 2 × CH₃), 1.35 (d, J 6.5 Hz, 3H, CH₃); δ_C: 166.8 (C, C-1), 111.0 (C), 110.4 (C), 77.6 (CH), 77.2 (CH), 73.8 (CH), 72.4 (CH), 70.8 (CH), 25.6 (CH₃), 25.3 (CH₃), 25.0 (CH₃), 22.2 (CH₃), 16.9 (CH₃); m/z 257 [100%, (M − CH₃)^•+], 128 (24), 113 (68), 83 (94).

7-Deoxy-L-glycero-D-mannoheptopyranose (6S-6C-methylmannose, 1). DIBAL-H (165 μl of a 1 M solution in hexane, 0.165 mmol) was added, dropwise, to a magnetically stirred solution of lactone 11 (15 mg, 0.05 mmol) in dichloromethane (1.0 ml) maintained at −78 °C under a nitrogen atmosphere. After a further 5 min, methanol (1.0 ml) was added, dropwise, to the reaction mixture which was then allowed to warm to 18 °C (over ca. 20 min) before being quenched with ammonium chloride (4 ml of a saturated aqueous solution). The resulting mixture was partitioned between ethyl acetate (5 ml) and brine (5 ml) and the separated aqueous layer extracted with ethyl acetate (3 × 5 ml). The combined organic layers were dried (Na₂SO₄), filtered and concentrated under reduced pressure to afford a pale-yellow oil (16 mg) which is presumed to contain lactol 12. This oil was immediately treated with trifluoroacetic acid (6 ml) and water (4 ml) and the resulting solution stirred at 18 °C for 16 h. After this time the reaction mixture was concentrated under reduced pressure to afford a pale-pink oil which was partitioned between water (5 ml) and diethyl ether (5 ml). The separated aqueous layer was washed with diethyl ether (2 × 5 ml) then freeze-dried to give compound 1³ (10 mg, 99%) as a white foam, [α]_D −10 [c 0.98 (in D₂O after 10 min)]. ν_max (KBr/cm⁻¹): 3424; δ_H: (500 MHz, D₂O) (α-anomer) 5.16 (d, J_1,2 1.7, 1H, H-1), 4.14 (dq, J_6,7 6.7, J_6,5 1.8, 1H, H-6), 3.88 (dd, J_2,3 3.1, J_2,1 1.7, 1H, H-2), 3.78 (dd, J_3,4 9.3, J_3,2 3.1, 1H, H-3), 3.74 (app t, J 9.3, 1H, H-4), 3.52 (dd, J_5,4 9.3, J_5,6 1.8, 1H, H-5), 1.22 (d, J_7,6 6.7, 3H, 7-CH₃); (β-anomer) 4.84 (d, J_1,2 1.0, 1H, H-1), 4.10 (dq, J_6,7 6.6 Hz, J_6,5 2.3, 1H, H-6), 3.89 (dd, J_2,3 3.5, J_2,1 1.0, 1H, H-2), 3.69 (app t, J 9.8, 1H, H-4), 3.60 (dd, J_3,4 9.8, J_3,2 3.5, 1H, H-3), 3.09 (dd, J_5,4 9.8, J_5,6 2.3, 1H, H-5), 1.25 (d, J_7,6 6.6 Hz, 3H, 7-CH₃); δ_C: (α-anomer) 94.8 (CH, C-1), 74.8 (CH), 71.9 (CH), 71.3 (CH), 67.5 (CH), 65.2 (CH), 19.5 (CH₃); (β-anomer) 94.6 (CH, C-1), 78.6 (CH), 74.0 (CH), 71.9 (CH), 67.2 (CH), 65.3 (CH), 19.4 (CH₃); m/z (ES) 411 (2M + Na)⁺, 217 (M + Na)⁺.

7-Deoxy-2,3: 5,6-di-O -isopropylidene-α-L-glycero-D-mannoheptofuranose (13). (1S)-(+)-10-Camphorsulfonic acid (1.6 mg, 0.01 mmol) was added to a stirred solution of compound 1 (11 mg, 0.06 mmol) in acetone (1.0 ml) maintained at 18 °C. After 16 h the reaction mixture was treated with sodium bicarbonate (ca. 30 mg) and after a further 1 h filtered through a no. 3 porosity sintered glass funnel. The filtrate was concentrated under reduced pressure to afford a colourless oil which was subjected to flash chromatography (1:2 ethyl acetate–hexane elution). Concentration of the appropriate fractions (R_f 0.4) afforded a colourless solid which was recrystallised (hexane) to give compound 13³ (10 mg, 64%) as colourless crystals, m.p. 118–119 °C (lit.³ m.p. 121–122 °C); [α]_D −2.8 [c 0.50 (after 10 min)]; HRMS: found: m/z 259.1180 (M − CH₃)^•+; C, 57.1; H, 8.0. C₁₃H₂₂O₆ requires 259.1182; C, 56.9; H, 8.1%. ν_max (KBr/cm⁻¹): 3503, 1061; δ_H: 5.38 (d, J 2.6, 1H), 4.85 (dd, J 5.8, 3.6, 1H), 4.61 (d, J 5.9, 1H), 4.15 (m, 1H), 4.06 (dd, J_4,5 8.8, 3.5, 1H), 3.87 (dd, J 8.7, 7.3, 1H), 2.36 (d, J 2.4, 1H, OH), 1.47 (s, 6H, 2 × CH₃), 1.39 (s, 3H, CH₃), 1.37 (d, J 6.1 Hz, 3H), 1.34 (s, 3H, CH₃); δ_C: 112.7 (C), 109.0 (C), 101.5 (CH, C-1), 85.3 (CH), 81.7 (CH), 80.0 (CH), 78.5 (CH), 76.7 (CH), 27.6 (CH₃), 26.9 (CH₃), 26.0 (CH₃), 24.8 (CH₃), 18.9 (CH₃); m/z 259 [60%, (M − CH₃)^•+], 199 (67), 149 (100).

7-Deoxy-2,3: 4,5-di-O-isopropylidene-D-glycero-D-mannoheptonic acid ε-lactone (14). Diol 9 (53 mg, 0.19 mmol) was oxidised under the same conditions as employed for the conversion 10 → 11. The colourless solid obtained on work-up was subjected to flash chromatography (1:4 ethyl acetate–hexane elution) which afforded, after concentration of the appropriate fractions (R_f 0.1), lactone 14 (45 mg, 86%) as colourless crystals, m.p. 161–163 °C; [α]_D −58.4 (c 1.20); HRMS: found: m/z 257.1024 (M − CH₃)^•+; C, 57.6; H, 7.4. C₁₃H₂₀O₆ requires 257.1025; C, 57.3; H, 7.4%). ν_max (KBr/cm⁻¹): 2989, 2928, 1760, 1378, 1203, 1077; δ_H: 4.96 (d, J 9.2, 1H), 4.50–4.30 (complex m, 2H), 4.10 (m, 2H), 1.59 (s, 3H, CH₃), 1.55 (s, 3H, CH₃), 1.52 (d, J 5.9 Hz, 3H), 1.42 (s, 3H, CH₃), 1.38 (s, 3H, CH₃); δ_C: 168.1 (C, C-1), 111.5 (C), 111.0 (C), 78.8 (CH), 77.7 (CH), 76.5 (CH), 73.7 (CH), 72.2 (CH), 28.0 (CH₃), 26.4 (CH₃), 25.4 (CH₃), 24.0 (CH₃), 18.8 (CH₃); m/z 257 [100%, (M − CH₃)^•+], 156 (21), 145 (46), 83 (40), 59 (93).

7-Deoxy--glycero--mannoheptopyranose (6R-6C-methylmannose, 2). DIBAL-H (165 μl of a 1 M solution in hexane, 0.165 mmol) was added dropwise to a solution of lactone 14 (15 mg, 0.05 mmol) in dichloromethane (1.0 ml) at −78 °C. After a further 5 min, methanol (1.0 ml) was added dropwise to the reaction mixture which was allowed to warm to 18 °C over ca. 20 min then treated with ammonium chloride (4 ml of a saturated aqueous solution). The resulting mixture was partitioned between ethyl acetate (5 ml) and brine (5 ml) and the separated aqueous layer extracted with ethyl acetate (3 × 5 ml). The combined organic layers dried (Na₂SO₄), filtered and concentrated under reduced pressure to afford a pale-yellow oil (16 mg) which is presumed to contain lactol 12. This oil was immediately treated with trifluoroacetic acid (6 ml) and water (4 ml) and stirred at 18 °C for 16 h. The resulting mixture was concentrated under reduced pressure to afford a pale-pink oil which was partitioned between water (5 ml) and diethyl ether (5 ml). The aqueous layer was washed with diethyl ether (2 × 5 ml) then freeze-dried to afford compound 2³ (10 mg, 99%) as a foam, [α]_D −13.8 [c 1.00 (in H₂O after 10 min)]. ν_max (KBr/cm⁻¹): 3434; δ_H: (500 MHz, D₂O) (α-anomer) 5.14 (d, J_1,2 2.0, 1H, H-1), 4.13 (dq, J_6,7 6.5, J_6,5 2.7, 1H, H-6), 3.89 (dd, J_2,3 3.5, J_2,1 2.0, 1H, H-2), 3.79(7) (dd, J_5,4 9.8, J_5,6 2.7, 1H, H-5), ), 3.78(7) (dd, J_3,4 9.8, J_3,2 3.5, 1H, H-3), 3.59 (app t, J 9.8, 1H, H-4), 1.20 (d, J_7,6 6.5, 3H, 7-CH₃); (β-anomer) 4.84 (d, J_1,2 1.0, 1H, H-1), 4.12 (dq, J_6,7 6.3, J_6,5 2.7, 1H, H-6), 3.90 (dd, J_2,3 3.0, J_2,1 1.0,† 1H, H-2), 3.60 (dd, J_3,4 9.5, J_3,2 3.0, 1H, H-3), 3.51 (t, J 9.5, 1H, H-4), 3.32 (dd, J_5,4 9.5, J_5,6 2.7, 1H, H-5), 1.21 (d, J_7,6 6.3 Hz, 3H, 7-CH₃); δ_C: (150 MHz, D₂O) (α-anomer) 94.7 (CH, C-1), 74.7 (CH), 71.2 (CH), 71.1 (CH), 68.6 (CH), 67.0 (CH), 15.9 (CH₃, C-7); (β-anomer) 94.5 (CH, C-1), 78.7 (CH), 73.8 (CH), 71.7 (CH), 68.3 (CH), 67.1 (CH), 15.9 (CH₃); m/z (ES) 411 (2M  + Na)⁺, 217 (M + Na)⁺.

Crystal data and refinement details for compounds 11, 13 and 14

Structure determination: images were measured on a Nonius Kappa CCD diffractometer (Mo-Kα, graphite monochromator, λ  = 0.71073 Å) and data extracted using the DENZO package.¹⁴ Structure solution was by direct methods (SIR92)¹⁵ and refinement was by full-matrix least squares on F using the maXus program package.¹⁶

CCDC reference number 440/227. See http://www.rsc.org/suppdata/nj/b0/b005312k/ for crystallographic files in .cif format.

Acknowledgements

We are grateful to the Institute of Advanced Studies for financial support and the Australian Research Council for provision of an APA(I) Scholarship (to D. J. W). Professor G. W. J. Fleet (Oxford University) is thanked for useful exchanges of information.

Notes and references

1. R. A. Dwek, Chem. Re[italic v]., 1996, 96, 683; A. Berecibar, G. Grandjean and A. Siriwardena, Chem. Re[italic v]., 1999, 99, 779; C. Wong, Angew. Chem., Int. Ed., 1999, 38, 2300.
2. R. Schwartz, ‘Inborn Errors of Carbohydrate Metabolism’, in Principles of Perinatal and Neonatal Metababolism, ed. R. M. Cowett, Springer, New York, 2nd edn., 1998, p. 723;; Chem. Abstr., 1998, 125, 159865..
3. A. Martin, M. P. Watterson, A. R. Brown, F. Imtiaz, B. G. Winchester, D. J. Watkin and G. W. J. Fleet, Tetrahedron: Asymmetry, 1999, 10, 355.
4. Y. Blériot, C. F. Masaguer, J. Charlwood, B. G. Winchester, A. L. Lane, S. Crook, D. J. Watkin and G. W. J. Fleet, Tetrahedron, 1997, 53, 15135; Y. Blériot, K. H. Smelt, J. Cadefau, M. Bollen, W. Stalmans, K. Biggadike, L. N. Johnson, N. G. Oikonomakos, A. L. Lane, S. Crook, D. J. Watkin and G. W. J. Fleet, Tetrahedron Lett., 1996, 37, 7155; Y. Blériot, C. Veighey, K. H. Smelt, J. Cadefau, W. Stalmans, K. Biggadike, A. L. Lane, M. Muller, D. J. Watkin and G. W. J. Fleet, Tetrahedron: Asymmetry, 1996, 7, 2761; C. F. Masaguer, Y. Blériot, J. Charlwood, B. G. Winchester and G. W. J. Fleet, Tetrahedron, 1997, 53, 15147.
5. For a comprehensive and up-to-date commentary on the production and synthetic utility of cis-1,2-dihydrocatechols, see T. Hudlicky, D. Gonzalez and D. T. Gibson, Aldrichim. Acta, 1999, 32, 35. Hudlicky et al. were the first to demonstrate the utility of cis-1,2-dihydrocatechols as starting materials for the preparation of carbohydrates. This group's elegant work in the area is covered in the following review articles: T. Hudlicky and J. W. Reed, in Ad[italic v]ances in Asymmetric Synthesis, ed. A. Hassner, JAI Press, Greenwich, CT, 1995, p. 271;; T. Hudlicky, D. A. Entwistle, K. K. Pitzer and A. J. Thorpe, Chem. Re[italic v]., 1996, 96, 1195.
6. For some leading references concerning the prospects of generating stable isotope-labelled carbohydrates from cis-1,2-dihydrocatechols, see M. G. Banwell, C. De Savi, D. C. R. Hockless, S. Pallich and K. G. Watson, Synlett, 1999, 885.
7. T. Hudlicky, H. Luna, G. Barbieri and L. D. Kwart, J. Am. Chem. Soc., 1988, 110, 4735.
8. M. Brovetto, V. Schapiro, G. Cavalli, P. Padilla, A. Sierra, G. Seoane, L. Suescun and R. Mariezcurrena, New J. Chem., 1999, 23, 549.
9. The ready cleavage of compound 7 contrasts with the behaviour of the chloro analogue 7′ which fails to react with ozone (see M. Banwell, C. De Savi and K. Watson, Chem. Commun., 1998, 1189)..
10. The crude reaction mixture derived from ozonolytic cleavage of alkene 7, and which is presumed to contain compound 8, gave a positive test for peroxides. ¹H NMR spectroscopic analysis of this reaction mixture suggests that compound 8 is obtained as a single diastereoisomer. Hudlicky et al. have reported (J. Am. Chem. Soc., 1994, 116, 5099) the isolation of related intermediates during the ozonolysis of similar alkenes..
11. R. Siedlecka, J. Skarzewski and J. Mlochowski, Tetrahedron Lett., 1990, 31, 2177.
12. W. C. Still, M. Kahn and A. Mitra, J. Org. Chem., 1978, 43, 2923.
13. D. D. Perrin and W. L. F. Amarego, Purification of Laboratory Chemicals, 3rd edn., Pergamon Press, Oxford, 1988..
14. DENZO-SMN. Z. Otwinowski and W. Minor, ‘Processing of X-ray diffraction data collected in oscillation mode’, in Methods in Enzymology Vol. 276: Macromolecular Crystallography, Part A, ed. C. W. Carter, Jr. and R. M. Sweets, Academic Press, New York, 1997, pp. 307–326..
15. A. Altomare, M. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Cryst., 1993, 26, 343.
16. S. Mackay, C. J. Gilmore, C. Edwards, M. Tremayne, N. Stuart and K. Shankland, maXus: a computer program for the solution and refinement of crystal structures from diffraction data, University of Glasgow, Scotland, Nonius BV, Delft, The Netherlands and MacScience Co. Ltd., Yokohama, Japan, 1998..

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Footnote

† Fleet et al. report³ that J_2,1  = 9.7 Hz for the β-anomer of compound 2. This is the only discrepancy between our NMR data sets and all those reported³ for each anomer of compounds 1 and 2. We believe Fleet's value for J_2,1 cited above to be in error.

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