SYNTHETIC PROCESS FOR HIGHLY FUNCTIONALIZED CARBOCYCLIC POLYOLS AND SUBSTITUTED SUGAR ANALOGS

Abstract: Chemical processes for more efficient synthesis of carbocyclic polyols and substituted sugar analogs are disclosed, together with a novel class of cyclopentene polyol intermediate products and anhydro derivatives thereof.

Description: SYNTHETIC PROCESS FOR HIGHLY FUNCTIONALIZED CARBOCYCLIC POLYOLS AND SUBSTITUTED SUGAR ANALOGS Technical Field of the Invention The present invention provides synthetic processes for shorter and more efficient syntheses of functionalized carbocyclic (polyol) compounds and substituted sugar analogs including novel classes of cyclopentene and cyclohexene polyol intermediates and derivatives thereof. Background of the Invention Fructose 2,6-bisphosphate (Figure 1, compound 1) is formed by phosphorylation of fructose 6-phosphate, a key substrate in the glycolysis pathway, in a reaction catalyzed by phosphofructokinases (PFK's) (Hasemann et al. Structure, 4:1017, 1996; Pilkis et al., Ann. Rev. Biochem. 64:799, 1995; and Rousseau et al, Nucl. Acid Res. Mol. Biol. 45:99, 1993). Fructose 2,6-bisphosphate is a key regulatory molecule for glycolysis and gluconeogenesis via its potent stimulatory effect on phosphofructokinase-1 activity and its inhibitory effect on fructose 1,6-bisphosphatase. The importance of this regulatory mechanism underscores the need for analogs of fructose 2,6-bisphosphate with which to probe and potentially control mechanisms that govern anaerobic glycolysis. To date, such controlled modulation of glycolysis has not been accomplished. In this regard, certain carbocyclic sugar analogs might be particularly useful. Accordingly, there is a need to generate carbocyclic sugar analogs efficiently, economically and in good yield. Ring closing metathesis (RCM) has recently become a powerful tool for the synthesis of medium (5-8) to large (10-13 and higher) carbo or heterocycles (Furstner and Langemann, Synthesis 792, 1997; Grubbs and Miller, Ace. Chem. Res. 28: 446, 1995; Nicaloau et al., J. Am. Chem. Soc 119:10073, 1997; Crimmins and Choy, J. Org. Chem. 62:7548, 1997; Schmalz, Angew. Chem. Int. Ed. Engl. 34:1833, 1995; and Arisawa et al., Syn. Lett. 1179, 1997). More recently there have been two reports dealing with RCM on functionalized substrates. The first is the synthesis of the six-membered poylsubstituted cyclohexene valiolamine employing Schrock's catalyst (Sellier et al., Tetrahedron Lett. 40:853, 1999) and the second is the synthesis of the seven-membered heterocyclic oxepine skeleton (Ovaa et al., Tetrahedron Lett. 39:3025, 1998) utilizing Grubbs' catalyst. Carbocyclic D-fructofuranoside (Figure 1 , compound 2) has been synthesized in twelve-steps with cyclopentane ring closure achieved by free radical-mediated cyclization (Wilcox and Guadino, J Am. Chem. Soc. 108:3102, 1986). This synthetic approach is difficult, provides low yields and is not useful for commercial synthesis. There is a need in the art to improve the synthesis of carbocyclic polyols and substituted analogs because such agents may be active in affecting intermediary metabolism (glycolysis). Summary of the Invention By controlling glycolysis, it may be possible to interfere with some diseases that manifest aberrant activity or flux in glycolytic pathways. Such diseases would include, for instance, insulin-dependent and non-insulin dependent diabetes mellitus (Nathan, Ann. Int. Med. 124:86, 1996; and Nishimura et al., J. Biol. Chem. 269:26100, 1994) and cancer (Chesney et al., Proc. Natl Acad. Sci. USA 6:3046, 1999; Argiles et al., J. Mol. Cell. Biochem. 81 :3, 1988; and Hue et al., Adv. Enz. Regul. 33:97, 1993). Unlike native carbohydrates such as phosphorylated fructose, carbocyclic sugar analogs cannot be metabolized and may therefore have prolonged effects on the control of glycolysis, offering the opportunity to interfere with or modulate both normal and pathological mechanisms that regulate glycolysis. The present invention provides an improved process for synthesis of carbocyclic sugar analogs by annulation of an olefinic intermediate. One embodiment of the inventive process provides an eight-step synthesis procedure that is a significant improvement over a twelve-step process published in 1986. Specifically, one embodiment of the invention provides a process (according to Scheme I) for synthesizing a class of desired intermediate products for further derivatization to provide final carbocyclic sugar analogs, comprising the steps of: (a) subjecting a pentose or a hexafuranose precursor compound that is not protected at the anomeric hydroxyl group to a Wittig reaction to effect ring opening and generate an alkene intermediate product; (b) oxidizing the alkene intermediate product of step (a) to yield a keto-alkene intermediate product; (c) effecting the nucleophilic addition of vinyl carbanion to the keto-alkene intermediate product of step (b) under Grignard conditions to provide a 1 ,6- heptadiene product; (d) optionally protecting the generated free alcohol of the 1,6-heptadiene product of step (c) to generate a fully protected 1,6-heptadiene product; (e) subjecting the 1,6-heptadiene product of step (c) or step (d) to ring closure metathesis (RCM) conditions with an RCM catalyst to effect ring closure and generate a functionalized cyclopentene product. This synthetic scheme is (Scheme I) summarized in Figure 2. The novel functionalized cyclopentene product of step (e) may then be deprotected and/or further functionalized or elaborated to provide carbocyclic sugar analog agents to probe, characterize and modulate glycolysis and the normal and pathological mechanisms that operate to control glycolysis in healthy and diseased individuals. For example, the functionalized cyclopentene product of step (e) is subjected to Sharpless epoxidation to provide a corresponding anhydro cyclopentane product advantageous for the generation of carbocyclic sugar analogs (Figure 3). Alternatively, at step (a), a series of reactions including sequential oxidation, methyl Grignard addition and acetylation followed by thionyl chloride elimination, optionally executed as a one-pot reaction, (according to Scheme II) may be substituted for the Wittig reaction to effect ring opening and generate an alkene intermediate product (see Figure 4). In a second alternative, a hexopyranose precursor compound is instead utilized at step (a) of Scheme I, and after step (b), the keto-alkene intermediate product is subjected to a Wittig reaction to provide a 1,6 heptadiene product that is suitable for step (e). In a further embodiment of the general method (see Figure 5), a hexopyranose precursor compound is utilized instead at step (a) of Scheme I, to provide a 1 ,7 octadiene intermediate product at step (c), such that the process provides a corresponding functionalized cyclohexene product (according to Scheme III, Figure 5): (a) subjecting a hexopyranose precursor compound (14) that is not protected at the anomeric hydroxyl group to a Wittig reaction to effect ring opening and generate an alkene intermediate product (15); (b) oxidizing the alkene intermediate product of step (a), 15, to yield a keto-alkene intermediate product (16); (c) effecting the nucleophilic addition of vinyl carbanion to the keto-alkene intermediate product of step (b), 16, under Grignard conditions to provide a 1,7- octadiene product (17); (d) optionally protecting the generated free alcohol of the 1,7-octadiene product of step (c) to generate a fully protected 1,7-octadiene product (18); (e) subjecting the 1,7-octadiene product of step (c), 17, or step (d), 18, to ring closure metathesis (RCM) conditions with an RCM catalyst to effect ring closure and generate a functionalized cyclohexene product (19). Any of the functionalized cyclopentene or cyclohexene products of step (e), from Scheme I, II, or III, are converted into corresponding carbacyclic sugar analogs. In some cases, this is accomplished by carbonylation (hydroformylation) followed by reduction, as described in detail in Example 9 and Scheme V with completion in Scheme VI, a process not previously demonstrated on highly functionalized polyol (i.e., polyhydroxylated) systems. Alternatively, the starting materials can be halo-sugars or azo-sugars. Preferably, any of the RCM catalysts above are selected from the group consisting of a Grubbs' catalyst and a Schrock's catalyst. More preferably, the protecting groups are benzyl or alkylsilyl groups, and combinations thereof. Still more preferably, the pentose precursor compound is 2,3,5-tri-O- benzyl-D-arabinofuranose. Brief Description of the Drawings Figure 1 shows the structure of fructose 2,6-bisphosphate (1) on the left and carbocyclic D-fructofuranoside (2) on the right. Figure 2 shows a scheme (Scheme I) using a ring closing metathesis (RCM) method for the synthesis of functionalized cyclopentene intermediate products adapted for further derivatization to generate carbocyclic sugar analogs and related polyols. Figure 3 shows a scheme for synthesis of functionalized anhydro cyclopentane intermediate products from the corresponding functionalized cyclopentene intermediate products shown in Figure 2. Figure 4 shows a scheme (Scheme II) using a ring closing metathesis (RCM) method for synthesis of methyl-substituted functionalized cyclopentene intermediate products adapted for further derivatization to generate carbocyclic sugar analogs and related polyols. Figure 5 shows a scheme (Scheme III) using a ring closing metathesis (RCM) method for synthesis of functionalized cyclohexene intermediate products adapted for further elaboration to generate carbocyclic sugar analogs and related compounds. Detailed Description of the Invention Wilcox and Guadino (J. Am. Chem. Soc 108:3102, 1986) have shown the first and only synthetic approach to carbocyclic D-fructofuranoside. The overall synthesis involved 12 steps. The cyclopentane ring closure was done via a free radical-mediated cyclization. The present invention provides a new and advantageous process for synthesis of carbocyclic sugar analogs by annulation of an olefinic intermediate via ring closing metathesis. In particular, we describe herein the synthesis of a polyhydroxylated cyclopentene, carbafructofuranose precursor (compound 8 in Figure 2) using RCM methodology. In this synthetic approach shown in Figure 2, compound 8 arises via RCM of a diene precursor, compound 7, which is readily assembled from an available carbohydrate derivative (compound 3 in Figure 2). Treatment of the commercially available 2,3,5-tri-O-benzyl-D-arabinofuranose (Freeman and Robarge, Carbohydr. Res. 154:270, 1986) (see Figure 2, compound 3) under Wittig and Swera conditions (briefly, BuLi (2.1 eq.), CH 3 PPh 3 + Br " (2.3 eq.), THF, 0 °C to RT, 87%, and then DMSO (5 eq.), Et 3 N (10 eq.), (COCl) 2 (4.8 eq.), CH 2 C1 2 , -78 °C to RT 90%) furnished compound 5 in 78% yield. Addition of vinylmagnesiumbromide (briefly CH 2 =CH 2 MgBr (1M in THF, 3 eq.), THF, -78 °C to 0 °C, 92%) afforded the single diene alcohol precursor (Figure 4, compound 6). The origin of the stereochemistry at this center cannot be readily predicted and is probably a result of the stereo-directing effect of the chiral α-benzyloxy group. The alcohol (compound 6) was subsequently protected as the benzyl ether (compound 7 of Figure 2; briefly BNBr (3 eq.), B ^NI (0.1 eq.), DMF 98%) and then subjected to RCM under Schrock's conditions (briefly, Schrock's catalyst (20 mmol%), CH 2 C1 2 , RT, 87%) yielding the novel functionalized cyclopentene intermediate product (compound 8 in Figure 2). The stereochemistry of the cyclic product was established using nuclear Overhauser effect (NOE) analysis. NOE analysis has previously been used in the structural assignment of similar five- and six-membered cyclic compounds (Sellier et al., Tetrahedron Lett. 40:853, 1999; and Seepersaud et al., Tetrahedron 53:5711, 1997). The 1H NMR signals of compound 8 were first identified by correlated spectroscopy (COSY). The NOE analysis allowed for structural assignment. An NOE of 1.5% between H 3 and one of the benzylic protons Hi and also a 1.0% NOE between H 6 and the other benzylic proton Hi was observed. These data provide strong support for a syn relationship between C-2/C-3 benzyloxy groups and assigns the framework of compound 8 with the correct stereochemistry at C-2, 3 and C-4 of compound 1 (Figure 1) since the stereochemistry at C-3 and C-4 was conserved. Note the protecting groups utilized according to the teachings herein may be chosen from among the many that are well-known in the chemical arts, such as benzyl, alkylsilyl, benzoyl, and acetyl. In summary we have demonstrated concise and efficient syntheses of functionalized cyclopentene and cyclohexene products, via a pathway that is generalized to a variety of starting pentoses and hexoses, to provide highly functionalized cyclic products. These functionalized cyclohexene and cyclopentene products, together with corresponding methyl- substituted and anhydro derivatives thereof, are themselves precursors adapted for subsequent derivatization or other elaboration to provide useful carbocyclic sugar analogs and related polyol compounds. A new approach comprising hydroformylation of the functionalized cycloalkenes generated as above, followed by reduction, yields the final carbocyclic sugar analogs and other carbacyclic polyol products in fewer steps than heretofor possible. Example 1 This example illustrates the synthesis of compound 4 (Figure 2) from 2,3,5-tri-O- benzyl-D-arabinofuranose (compound 3, Figure 2). For the following syntheses, thin layer chromatography (TLC) was carried out on aluminum sheets precoated with silica gel 60 (HF- 254, E. Merck) to a thickness of 0.25 mm. Flash column chromatography (FCC) was performed using Kieselgel 60 (230-400 mesh, E. Merck) and usually employed a stepwise solvent polarity gradient, correlated with TLC mobility. H and C NMR spectra were obtained on JEOL 270 instrument. Unless otherwise noted, spectra were recorded at 270 and 67.5 MHz respectively. Mass spectral analyses were performed by mass spectrometral facilities of Hunter College and University of Illinois. Dry THF was obtained by distillation, under nitrogen from potassium-benzophenon ketyl. Dichloromethane was distilled from P 2 O . Other solvents were purified and dried by using standard procedures. nBuLi (11.0 mmole, 1.6 M in Hexane) was added to a suspension of methyl triphenylphosphonium bromide (4.28 g, 12.0 mmol) in dry THF (25 mL) at 0 °C under N 2 . The suspension was allowed to stir for 30 min at 0 °C then warmed up to RT (1 h). 2,3,5-tri-O- benzyl-D-arabinofuranose (compound 3; 2.0 g, 5 mmol) was dissolved in THF (5 mL) and transferred by cannula dropwise over 10 min. The reaction mixture was allowed to warm to RT, followed by addition of Et 2 O (100 mL). The suspension was filtered through celite and excess solvent evaporated. FCC (10% - 30% EtOAc : PE ) furnished a clear oil, compound 4 of Figure 2 (1.81 g, 87%). Rf 0.6 (20% EtOAc : PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.34 (m, 15H), 5.95 (m, 1H), 5.34 (m, 2H), 4.62 (ABq, Δδ = 0.09 ppm, 2H, J = 11.9 Hz), 4.52 (m, 2H), 4.50 (ABq, Δδ = 0.23 ppm, 2H, J = 11.2 Hz), 4.1 (m, IH), 4.04 (m, IH), 3.64 (m, 3H). 13 C NMR (67.5 MHz, CDC1 3 ) δ 138.3, 138.2, 138.0, 135.2, 128.5-127.8 (8 signals), 119.2, 80.6, 74.2, 73.5, 71.0, 70.8, 70.5. Example 2 This example illustrates the synthesis of compound 5 from compound 4 (see Figure 2). To a solution of oxalyl chloride (549 mg, 4.3 mmol) in anhydrous CH 2 C1 2 (5 mL) at -78 °C under N was added DMSO (375 mg, 4.8 mmol) and the mixture allowed to stir for 20 min. The alcohol, compound 4, [200 mg, 0.48 mmol, dissolved in CH 2 C1 2 (4 mL)] was then added and the reaction allowed to stir for 25 min. Et 3 N (847 mg, 8.6 mmol) was then added and the solution warmed to 0°C. Et 2 O (50 mL) was added and the combined organic washed with saturated aqueous NaHCO (30 mL), brine (30 mL) and dried (MgSO 4 ). The Et 2 O extract was concentrated in vacuo and purified by FCC (10-40% EtOAc :PE), to give the ketone, compound 5 (179 mg, 90%). Rf 0.75 (25% EtOAc : PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.30 (m, 15H), 5.91 (m, IH), 5.33 (m, IH), 4.48-4.60 (m, 4H), 4.35 (m, 2H), 4.28 (m, 2H), 4.19 (m, IH), 4.00 (d, IH, J = 3.5 Hz). 13 C NMR (67.5 MHz, CDC1 3 ) δ 207.7, 137.6, 137.5, 136.9, 134.2, 128.6- 127-8 (6 signals), 119.9, 85.9, 81.0, 74.7, 73.4, 71.0. MS (ES) m/z 439 (M + Na + ), 434.2 (M + NH4 + ), 181 (base peak). Example 3 This example illustrates the synthesis of compound 6 from compound 5 (as shown in Figure 2). The azeotropically dried ketone (compound 5; 190 mg, 0.5 mmol) intermediate was dissolved in THF (5 mL), then cooled to -78 °C. A I M solution of vinylmagnesiumbromide (1.40 mmol, 1.4 mL) was then added dropwise and the solution was allowed to warm up to 0 °C. The reaction was quenched by addition to cold saturated NH 4 C1 (15 mL). The mixture was extracted with Et O (3 x 20 mL), washed with saturated aqueous NaHCO 3 (30 mL), brine (30 mL) and dried (MgSO 4 ). The Et O extract was concentrated in vacuo and purified by FCC (20-60% EtOAc : PE) to give the alcohol, compound 6 of Figure 2 (204 mg, 92%). Rf 0.4 (10% EtOAc : PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.32 (m, 15H), 6.17 (dd, IH, J = 1.7, 17.3 Hz), 5.99 (m, IH), 5.45 (dd, IH, J = 1.7, 17.3 Hz), 5.3 (m, 2H), 5.17 (dd, IH, J = 1.7, 10.6 Hz), 4.67 (ABq, Δδ = 0.07 ppm, 2H, J = 11.1 Hz), 4.42 (ABq, Δδ = 0.34 ppm, 2H, J = 11.4 Hz), 4.45 (m, 2H), 4.18 (dd, IH, J = 2.2, 8.2 Hz), 3.72 (d, IH, J = 2.2 Hz), 3.79 (d, IH, J = 8.4 Hz), 3.25 (d, IH, J = 8.4 Hz). 13 C NMR (67.5 MHz, CDC1 3 ) δ 140.3, 138.2, 138.1, 137.3, 136.1, 128.7-127.7 (7 signals), 118.9, 114.5, 82.0, 81.6, 78.3, 76.0, 74.4, 73.5, 70.6. MS (ES) m/z 467 (M + Na + ), 181 (base peak). Example 4 This example illustrates the synthesis of compound 7 from compound 6 (as shown in Figure 2). The alcohol intermediate (compound 6) (80 mg, 0.18 mmol) was dissolved in DMF (3 mL, anhydrous) and the solution was cooled to 0 °C and NaH (35 mg, 0.88 mmol) was added. Bu NI (13 mg, 0.036 mmol) followed by BnBr (156 mg, 0.9 mmol) was then added and the reaction mixture allowed to stir for 30 min. The reaction was quenched by dropwise addition of MeOH (2mL), then water (15 mL) and the aqueous mixture was extracted with Et O (3 x 15 mL). The combined Et O extract was washed with saturated aqueous NaHCO (10 mL), brine (10 mL) and excess solvent evaporated to give the tetrabenzylated product, compound 7 of Figure 2 (94 mg, 98%). Rf 0.7 (10% EtOAc:PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.33 (m, 20H), 6.08 (dd, IH, J = 10.6, 18.0 Hz), 6.01 (m, IH), 5.34 (d, IH, J = 1.7 Hz), 5.28 (m, 2H), 5.22 (m, IH), 4.74 (ABq, Δδ = 0.08 ppm, 2H, J = 11.1 Hz), 4.53 (ABq, Δδ = 0.11 ppm, 2H, J = 11.6 Hz), 4.4 (ABq, Δδ = 0.36 ppm, 2H, J - 11.9 Hz), 4.34 (m, 2H), 4.11 (dd, IH, J = 3.0, 7.7 Hz), 3.82 (d, IH, J = 10.9 Hz), 3.76 (d, IH, J = 3.2 Hz), 3.52 (d, IH, J = 10.9 Hz). 13 C NMR (67.5 MHz, CDC1 3 ) δ 139.8, 138.9, 138.2, 138.1, 137.3, 137.2, 128.5-127.0 (9 signals), 117.7, 116.1, 86.7, 82.8, 79.8, 76.3, 73.3, 70.2, 70.1, 65.1. MS (ES) m/z 557 [(M + Na + ), (base peak)], 535 (M + H + ). Example 5 This example illustrates the synthesis of compound 8 from compound 7 using RCM under Schrock's conditions (see Figure 2). The diene, compound 7, (70 mg, 0.131 mmol) dissolved in anhydrous CH 2 C1 (1.0 mL) was added to a homogeneous orange-red solution of Schrock's catalyst 2,6-diisopropylphenylimido neophylidenemolybdenum (VI) bis(hexafluoro-t- butoxide) (20 mg, 0.026 mmol) in anhydrous CH 2 C1 2 (4 mL) under N 2 . The resulting mixture was stirred at 20 °C for 18 h, at which time TLC showed formation of new material. The reaction mixture was quenched by exposure to air for 2 h then excess solvent evaporated in vacuo. The brown residue was purified by FCC (5-10% EtOAc : PE) to give the alkene, compound 8 (57.6 mg, 87%). %). Rf 0.5 (10% EtOAc : PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.25 (m, 20H), 6.05 (d, IH, J = 6.0 Hz, H-5), 5.77 (d, IH, J = 6.0 Hz, H-6), 4.78 (m, IH), 4.70 (m, IH, H-4), 4.56-4.46 (m, 6H), 4.34 (m, IH), 4.05 (d, IH, J = 4.0 Hz, H-3), 3.57 (ABq, Δδ = 0.07 ppm, 2H, J = 9.5 Hz, H-1). 13 C NMR (67.5 MHz, CDC1 3 ) δ 139.5, 138.7, 138.4, 138.3, 135.5, 134.0, 128.5-126.2 (8 signals), 89.1, 87.5, 84.7, 75.0, 73.6, 72.8, 71.6, 67.2. HRMS (FABMS) Calculated for C 34 H 34 O 4 (M+ H + ) 507.253535, found 507.253500. Example 6 This example illustrates an alternative synthesis of compound 8 from compound 7 using RCM under Grubbs' conditions. The diene (compound 7) (40 mg, 0.075 mmol) was dissolved in anhydrous CH 2 C1 2 (1.0 mL) and was added to a homogeneous orange-red solution of bis(tricyclopentylphosphine)benzylidine ruthenium dichloride (6.2 mg, 0.075 mmol) in anhydrous CH 2 C1 (2.5 mL) under N 2 . The resulting mixture was stirred at 20 °C for 48 h, at which time TLC showed formation of new material. The reaction mixture was quenched by exposure to air for 2 h then excess solvent evaporated in vacuo. The black residue was purified by FCC (5-10% EtOAc:PE) to give the diene (19.6 mg, 49%) and the carbafructofuranose precursor, compound 8, (13.3 mg, 35%). Rf 0.5 (10% EtOAc : PE); 1H NMR (270 MHz, CDC1 3 ) δ 7.25 (m, 20H), 6.05 (d, IH, J = 6.0 Hz, H-5), 5.77 (d, IH, J = 6.0 Hz, H-6), 4.78 (m, IH), 4.70 (m, IH, H-4), 4.56-4.46 (m, 6H), 4.34 (m, IH), 4.05 (d, IH, J = 4.0 Hz, H-3), 3.57 (ABq, Δδ = 0.07 ppm, 2H, J = 9.5 Hz, H-1). 13 C NMR (67.5 MHz, CDC1 3 ) δ 139.5, 138.7, 138.4, 138.3, 135.5, 134.0, 128.5-126.2 (8 signals), 89.1, 87.5, 84.7, 75.0, 73.6, 72.8, 71.6, 67.2. HRMS (FABMS) Calculated for C 34 H 34 O 4 (M+ H + ) 507.253535, found 507.253500. Example 7 This example illustrates the synthesis of a class of methyl-substituted cyclopentene intermediate products (compound 13, Figure 4), beginning with the same starting material (compound 3) as above. The synthetic scheme shown in Figure 4 replaces the Wittig reaction of step a in Figure 2 with a series of reactions including sequential oxidation, methyl Grignard addition and acetylation followed by thionyl chloride elimination (optionally executed as a one-pot reaction) to effect ring opening and generate an alkene intermediate product, compound 10 (see Figure 4). Briefly, the one-pot reaction involved oxidation of the 2,3,5-tri- O-benzyl-D-arabinofuranose starting material with 2,2,6,6-tetramethyl-l-piperidinyloxy free radical (TEMPO), methyl Grignard addition and acetylation followed by thionyl chloride elimination under standard conditions to furnish the diene, compound 10 in 88% yield. Deacetylation followed by oxidation under conditions described for the analogous step in the scheme of Figure 2, afforded the ketone, compound 11 in 96% yield. Addition of vinylmagnesiumbromide (as per scheme in Figure 2) afforded the single diene alcohol precursor that was subsequently benzylated to provide compound 12 (Figure 4). A single stereoisomer was obtained as in the above-described synthesis (Figure 2). The benzyl ether was then subjected to RCM conditions. Briefly, the diene, compound 12 (45 mg, 0.082 mmol) dissolved in anhydrous hexane (1.0 mL) was added to a homogeneous orange-red solution of Schrock's catalyst 2,6-diisopropylphenylimido neophylidenemolybdenum (VI) bis(hexafluoro- t-butoxide) (20 mg, 0.026 mmol) in anhydrous hexane (3 mL) under N 2 . The resulting mixture was refluxed at 90°C for 18 h, at which time TLC showed formation of new material. The reaction mixture was quenched by exposure to air for 2 h then excess solvent evaporated in vacuo. The brown residue was purified by FCC (5-10% EtOAc : PE) to give the alkene, compound 13 (34 mg, 81%). Example 8 The above-described novel application of RCM methodology to highly functionalized substrates was additionally employed in the total synthesis of carbacyclic D-fructofuranoside, in which the fully protected 1,6 heptadiene product of step (d) in Scheme II (compound 12) was oxidized by selenium oxide (SeO 2 ) and tert-butyl hydrogen peroxide (TBHP) to produce the corresponding alcohol. Following benzyl protection, the fully protected 1 ,6 heptadiene product was subjected to RCM to effect ring closure and generate the functionalized cyclopentene product. Deprotection and hydrogenation of the olefin in the presence of hydrogen and palladium provided the desired carbacyclic D-fructofuranoside in 11 steps in overall yield of 45% from the 2,3,5-tri-O-benzyl-D-arabinofuranose starting material (compound 3, Figure 2). (Seepersaud and Al-Abed, Organic Letters 1:1463-1465, 1999). Example 9 To shorten the synthesis and improve the yield of the desired carbacyclic D- fructofuranoside from the 2,3,5-tri-O-benzyl-D-arabinofuranose starting material (11 steps in overall yield of 45%; Example 8 above), we employed carbonylation methods not previously thought to be compatible with highly functionalized polyol systems. To provide a more efficient synthesis of carbafructofuranose (compound 2) involving fewer steps, we chose the cyclopentene (compound 8) as an attractive starting point because it possessed all the required functionality except at the C-5 position. What was needed was a one C extension at C-5 to give the hydroxymethyl group. Our strategy would also facilitate selective phosphorylation of C-2/C-6 to resemble the F2,6 BP target (compound 2), differentiating between the conserved protected hydroxyl groups and those generated by the hydroformylation (Scheme IV). Hydroformylation reactions on simple terminal and partially functionalized substrates have been well investigated, but there have been no reported examples of formylation on polyhydroxylated cyclic substrates. Carbonylation was accomplished according to Scheme V: (a) 5 steps, 90% (b) Wilkinson's catalyst, CO, H 2 , 8θPC, 24h, 99%. The hydroformylation reaction was carried out utilizing Wilkinson's catalyst [(Ph3P)3RhCl] in a mixture of carbon monoxide (40 bar) and hydrogen (40 bar) at 80 ^C for 24 h. Under these reaction conditions the functionalized cyclopentene was converted quantitatively to the corresponding aldehyde. The mixture of aldehydes (compounds 20 and 21) was then treated under reducing conditions (NaBH 4 / MeOH) to furnish the corresponding alcohols. These alcohols subsequently were separated by flash column chromatography to afford compound 22, together with two elimination products, 23 and 24. (Note that with alternative starting materials, a fourth potential product analogous to the regioisomer of 22 would also be expected.) Hydrogenation of compound 22 furnished the desired carbafructofuranose (compound 2); hydrogenation of 23 and 24 also provides sugar analogs (perhaps more properly deoxy sugar analogs) useful in screening for compounds of desired bioactivity, such as enzyme inhibition. Mass spectral and NMR data confirmed the identity of compounds 2, 22, 23 and 24 (Scheme VI). Scheme VI 20 21 21 t 24 (a) NaBH 4 , MeOH, 99%, (b) Pd/H 2 , EtOH, 98% 2 To date, this is the first reported example of the hydroformylation of a highly functionalized cyclopentene. Using this process, carbacyclic D-fructofuranoside was synthesized in 8 steps with a yield of 36%. This method (including importantly the preparation of a protected diene system, followed by RCM ring closure, followed by hydroformylation of the protected, highly functionalized cycloalkene intermediate products) is functional with other highly functionalized five- and six-membered cycloalkenes to provide a variety of carbacyclic analogs of naturally occurring sugars and their epimers. Also, the method is functional to produce less highly functionalized cyclic polyols, such as the carba analogs of deoxy sugars or the pentenomycins and their kin, simply by beginning with the appropriate polyol precursor compound. Moreover, libraries of diverse carbacyclic polyols can be produced simply by providing diverse polyol precursor compounds. Example 10 The pentenomycin antibiotics have attracted considerable attention due to their wide range of structural and stereochemical features and biological activities. Pentenomycin was isolated by Umino and co-workers in 1973 from the culture broths of Streptomyces eurythermus, while epipentenomycin the C-4 diastereomer, was isolated from carpophores of Perziza sp. There have been several approaches to synthesize these antibiotics and their derivatives however, an expeditious and efficient approach is still needed. Pentenomycin: A comparison of cyclopentene 8 with pentenomycin indicates that the stereochemistries around the C-4 and C-5 are identical. Therefore, the cyclopentene intermediate 8 was converted to pentenomycin by the following series of reactions: starting compound 8 was treated with BH3:THF to give the corresponding two regioisomeric alcohols; the desired alcohol was purified and oxidized by pyridinium chlorochromate to afford the corresponding ketone; the ketone was hydrogenated, then treated with pyridine/acetic anhydride to furnish the acetylated enone; deprotection of the acetate with trifluoroacetic acid/H2θ afforded (-)- pentenomycin. The *H and ^C NMR of the final product was identical with those reported in the literature for (-)-pentenomycin. In summary, a concise and efficient synthesis of the (-)- pentenomycin was demonstrated in 5 steps (46% yield), using the key polyhydroxy cyclopentene intermediate 8.

Claims: We claim: 1. A process for synthesizing carbocyclic sugar analogs comprising the steps of: (a) subjecting a pentose or a hexafuranose precursor compound (starting material) that is not protected at the anomeric hydroxyl group to a Wittig reaction to effect ring opening and generate an alkene intermediate product; (b) oxidizing the alkene intermediate product of step (a) to yield a keto-alkene intermediate product; (c) effecting the nucleophilic addition of vinyl carbanion to the keto-alkene intermediate product of step (b) under Grignard conditions to provide a 1,6-heptadiene product; (d) optionally protecting the generated free alcohol of the 1,6-heptadiene product of step (c) to generate a fully protected 1,6-heptadiene product; (e) subjecting the 1,6-heptadiene product of step (c) or step (d) to ring closure metathesis (RCM) conditions with an RCM catalyst to effect ring closure and generate a functionalized cyclopentene product adapted for subsequent derivatization to a carbocyclic sugar analog. 2. The process according to claim 1 for synthesizing the functionalized cyclopentene product of step (e), wherein the protecting groups are benzyl such that the pentose precursor compound (starting material) is 2,3,5-tri-O-benzyl-D-arabinofuranose. 3. The process according to claim 1 for synthesizing the functionalized cyclopentene product of step (e), wherein the ring closing metathesis (RCM) catalyst is chosen from the group consisting of a Schrock's catalyst and a Grubbs' catalyst. 4. The process according to claim 1 for synthesizing a functionalized anhydro cyclopentane product comprising the further step of derivatizing the functionalized cyclopentene product of step (e) by Sharpless epoxidation. 5. A functionalized cyclopentene product adapted for derivatization to a carbocyclic sugar analog according to the formula: wherein R is a protecting group selected from the group consisting of benzyl (Bn), alkylsilyl, benzoyl, and acetyl. 6. The functionalized cyclopentene product of claim 5 that is: 7. A functionalized anhydro cyclopentane product adapted for derivatization to a carbocyclic sugar analog according to the formula: wherein R is a protecting group selected from the group consisting of benzyl (Bn), alkylsilyl, benzoyl, and acetyl. 8. The functionalized anhydro cyclopentene product of claim 7 that is: 9. A process for synthesizing carbocyclic sugar analogs comprising the steps of: (a) subjecting a pentose or a hexafuranose precursor compound (starting material) that is not protected at the anomeric hydroxyl group to a series of reactions including sequential oxidation, methyl Grignard addition and acetylation followed by thionyl chloride elimination to effect ring opening and generate an alkene intermediate product; (b) oxidizing the alkene intermediate product of step (a) to yield a keto-alkene intermediate product; (c) effecting the nucleophilic addition of vinyl carbanion to the keto-alkene intermediate product of step (b) under Grignard conditions to provide a 1 ,6- heptadiene product; (d) optionally protecting the generated free alcohol of the 1,6-heptadiene product of step (c) to generate a fully protected 1,6-heptadiene product; (e) subjecting the 1,6-heptadiene product of step (c) or step (d) to ring closure metathesis (RCM) conditions with an RCM catalyst to effect ring closure and generate a functionalized cyclopentene product adapted for subsequent derivatization to a carbocyclic sugar analog. 10. A functionalized cyclopentene product adapted for derivatization to a carbocyclic sugar analog according to the formula: wherein R is a protecting group selected from the group consisting of benzyl (Bn), alkylsilyl, benzoyl, and acetyl. 11. The functionalized cyclopentene product of claim 10 that is: 12. A process for converting a cyclopentene or a cyclohexene having a plurality of stereo-specific substitutions to the corresponding aldehyde, comprising hydroformylating the cyclopentene or cyclohexene with carbon monoxide and hydrogen (H 2 ) in the presence of a catalyst. 13. The process of claim 12 wherein the substitutions are hydroxyl. 14. The process of claim 12 wherein the catalyst is Wilkinson's catalyst. 15. The process of claim 12 further comprising reducing the aldehyde group to a corresponding alcohol to form a stereospecific cyclic polyol. 16 An intermediate for synthesizing stereospecific cyclic polyols comprising a compound selected from the group consisting of protected compounds 20, 21, 22, 23, 24, deprotected 20, deprotected 21, deprotected 23, and deprotected 24 (all Scheme VI). 17. A process for generating a library of multiple carbocyclic sugar analogs, comprising subjecting multiple terminal diene compounds having protected hydroxyl groups to ring closure metathesis (RCM) conditions with an RCM catalyst to effect ring closure to generate a library of multiple cyclo-alkene products. 18. The process of claim 17 further comprising hydroformylating the library multiple cyclo-alkene products with carbon monoxide and hydrogen (H 2 ) in the presence of a catalyst to generate a library of corresponding aldehyde compounds.

Inventors: AL-ABED YOUSEF, SEEPERSAUD MOHINDRA, AL-ABED, YOUSEF, SEEPERSAUD, MOHINDRA
Applicants: PICOWER INST MED RES, THE PICOWER INSTITUTE FOR MEDICAL RESEARCH
Application year: 2000
Main classification: C07H1
IPC codes: C07B61, C07C29, C07C41, C07C43, C07C45, C07C49, C07D303, C07H1