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For over 50 years, our group has been involved in synthetic studies on biologically active cyclitols including carbasugars. Among a variety of compounds synthesized, this review focuses on carbaglycosylamine glycosidase inhibitors, highlighting the following: (1) the naturally occurring N-linked carbaoligosaccharide α-amylase inhibitor acarbose and related compounds; (2) the novel synthetic β-glycosidase inhibitors, 1'-epi-acarviosin and its 6-hydroxy analogue as well as β-valienaminylceramide and its 4'-epimer; (3) the discovery of the β-glycosidase inhibitors with chaperone activity, N-octyl-β-valienamine (NOV) and its 4-epimer (NOEV); and (4) the recent development of the potential pharmacological chaperone N-alkyl-conduramine F-4 derivatives.

This review describes the results of synthetic studies undertaken by the authors of this chapter on carbasugars over the last 30 years or so. These studies took advantage of the long-anticipated discovery of a sole crystalline cycloaddition adduct, which under favorable conditions could play a reliable role in laying down the foundation stone for the synthetic carbasugar chemistry. Although glycosidase inhibitors with chaperone activity have recently been evaluated as if they were a final goal, it seems from another synthetic point of view that the results accumulated have made total synthesis of natural carbaoligosaccharide validamycins and acarbose possible.

The development of second-generation valienamine-type chemical chaperones for GM1-gangliosidosis is described. Several N-substituted (+)-conduramine F-4 derivatives were designed as novel chemical chaperones based on a lead chaperone compound, N-octyl-4-epi-β-valienamine, to decrease the inhibitory activity while increasing the enzyme enhancement activity. Among the derivatives synthesized during this study, a conduramine derivative with an N-cyclohexylmethyl group has demonstrated significant enhancement of R201C mutated β-galactosidase activity.

This article reviews synthesis and structures of carbaglycosylamines, a group of carbocyclic sugar analogues. Some unsaturated derivatives are known to be potent glycosidase inhibitors. Among them, N-octyl-4-epi-beta-valienamine as a lysosomal beta-galactosidase inhibitor is currently undergoing a new molecular therapeutic trial (chemical chaperone therapy) for control of the human beta-galactosidase deficiency disorder, G(M1)-gangliosidosis.

β-Galactosidase deficiency is a group of lysosomal lipid storage disorders with an autosomal recessive trait. It causes two clinically different diseases, G(M1) -gangliosidosis and Morquio B disease. It is caused by heterogeneous mutations in the GLB1 gene coding for the lysosomal acid β-galactosidase. We have previously reported the chaperone effect of N-octyl-4-epi-β-valienamine (NOEV) on mutant β-galactosidase proteins. In this study, we performed genotype analyses of patients with β-galactosidase deficiency and identified 46 mutation alleles including 9 novel mutations. We then examined the NOEV effect on mutant β-galactosidase proteins by using six strains of patient-derived skin fibroblast. We also performed mutagenesis to identify β-galactosidase mutants that were responsive to NOEV and found that 22 out of 94 mutants were responsive. Computational structural analysis revealed the mode of interaction between human β-galactosidase and NOEV. Moreover, we confirmed that NOEV reduced G(M1) accumulation and ameliorated the impairments of lipid trafficking and protein degradation in β-galactosidase deficient cells. These results provided further evidence to NOEV as a promising chaperone compound for β-galactosidase deficiency.

Gaucher's disease (GD), mainly caused by a defect of acid beta-glucosidase (beta-Glu), is the most common form of sphingolipidosis. We have previously shown that the carbohydrate mimic and inhibitor of beta-Glu, N-octyl-beta-valienamine (NOV), could increase the protein level and enzyme activity of various mutant beta-Glus in cultured GD fibroblasts and in COS cells, suggesting that NOV acts as a pharmacological chaperone to accelerate transport and maturation of these mutant enzymes. In present study, we continued to investigate the chaperone characteristics of NOV. More importantly, chaperone activities of NOV were evaluated in COS cells transiently expressing ten new, recombinant beta-Glu mutants with mutations located in domain I, II and III. NOV was only effective on the T369M mutation, located in domain III. As we suggested in a previous study, domain III may be a prerequisite for pharmacological rescue of the mutant beta-Glu by NOV. These characteristics of NOV could provide potential therapeutic chaperone properties that would be useful in the treatment of GD with neurological manifestations due to gene mutations in beta-Glu.

Chemical chaperone therapy is a strategy for restoring the activities of mutant lysosomal hydrolases. This therapy involves chemical compounds binding to the dysfunctional enzymes. The chemical chaperones for lysosomal hydrolases are anticipated to stabilize folding of target enzymes by binding at neutral pH and rescuing enzyme activities by dissociation in acidic conditions after transport to lysosome. However, the molecular basis describing the mechanism of action of chemical chaperones has not been analysed sufficiently. Here we present results derived from molecular dynamics simulations showing that the binding free energy between human ?-glucosidase and its known chemical chaperone, N-octyl-?-valienamine (NOV), is lower at pH 7 than at pH 5. This observation is consistent with the hypothetical activity of chemical chaperones. The pH conditions were represented as differences in the protonation states of ionizable residues which were determined from predicted pKa values. The binding free energy change is negatively correlated to the number of hydrogen bonds (H-bonds) formed between GLU235, the acid/base catalyst of the enzyme, and the N atom of NOV. At pH 7, NOV is inserted further into the active site than at pH 5. Consequently, this provides an increase in the number of H-bonds formed. Thus, we conclude that the dissociation of NOV from ?-glucosidase at pH 5 occurs due to an increase in the binding free energy change caused by protonation of several residues which decreases the number of H-bonds formed between NOV and the enzyme.

3,8-Dioxatricyclo[3.2.1.0 2,4 ]octane-6-carboxylic acid, whose racemic form is readily available on a large scale, is a versatile starting material for the synthesis of carbasugars and carbocyclic biologically active natural products. In this study, the enzyme-catalyzed kinetic resolution was attempted on a variety of corresponding carboxylic esters. The hydrophobic and hydrophilic properties of ester substituents greatly affected the rate of reaction and the enantioselectivity. Hydrolysis of the corresponding 2′-chloroethyl ester with pig liver esterase worked well in a highly enantioselective manner ( E = 116) to give the hydrolyzate (90.6% ee) and unreacted ester recovery (99.4% ee). The hydrolyzate is a precursor for (−)-oseltamivir phosphate, and a route to (3 S ,4 S ,5 R )-(−)-3-epishikimic acid was developed from the recovered ester.

5a-Carba-alpha-D-glucopyranosylamine, validamine, and analogous compounds valienamine and valiolamine, have proved to be important lead compounds for development of clinically useful medicines, including the very strong alpha-glucosidase inhibitor, voglibose, N-(1,3-dihydroxyprop-2-yl)valiolamine, now used widely as a clinically important antidiabetic agent. In this review, we describe recent advances in development of glycosidase inhibitors on the basis of the ground-state mimics of the postulated glycopyranosyl cation, considered to be formed during hydrolysis of glycopyranosides, and introduce a new type of highly potent alpha-fucosidase inhibitor, 5a-carba-alpha-L-fucopyranosylamine, alpha-fuco validamine. Interestingly, the corresponding beta-anomer, and in particular its D-enantiomer, has been shown to possess very strong cross-inhibitory activity toward beta-galactosidase and beta-glucosidase. Structure and inhibitory activity relationships concerning these alpha,beta-fuco derivatives, as well as parent alpha,beta-galacto validamines are discussed here with reference to our results.

We performed screening of beta-galactosidase-deficient fibroblasts for possible chemical chaperone therapy using N-octyl-4-epi-beta-valienamine (NOEV) in patients with GM1-gangliosidosis and Morquio B disease (beta-galactosidosis). Fibroblasts were cultured with NOEV for 4 days and beta-galactosidase activity was measured. Mutation analysis was performed simultaneously. Two separate criteria were set for evaluation of the chaperone effect: a relative increase of enzyme activity (more than 3-fold), and an increase up to more than 10% normal enzyme activity. Among the 50 fibroblast strains tested, more than 3-fold increase was achieved in 17 cell strains (34%), and more than 10% normal activity in 10 (20%). Both criteria were satisfied in 6 (12%), and either of them in 21 (42%). Juvenile GM1-gangliosidosis was most responsive, and then infantile GM1-gangliosidosis. This enhancement was mutation-specific. We estimate that the NOEV chaperone therapy will be effective in 20-40% of the patients, mainly in juvenile and infantile GM1-gangliosidosis patients. A molecular design may produce mutation-specific chaperone compounds for the other disease phenotypes. This cellular screening will be useful for identification of human patients with beta-galactosidase deficiency for chaperone therapy to be started in the near future.

Coupling of 1,2-anhydro-3-O-benzyl-4,6-O-benzylidene-5a-carba-β-D-mannopyranose (3) with 1,6-anhydro-2,3-O-isopropylidene-β-D-mannopyranose (4) afforded a 5a′-carba disaccharide derivative linked by an ether bridge with α-manno configuration. This compound 5 was transformed into three stereoisomers in regard to the configurations at C-1′ and C-2′. Thus, the free 2′-hydroxyl group was oxidized, and the resulting ketone 8 was isomerized at C-1′ to 11 by treatment with potassium tert-butoxide. Reduction of the ketones 8 and 11 with l-selectride afforded selectively the synthetic useful intermediate ether-linked 5a′-carba disaccharides 9, 12, and 14 with α-gluco, β-gluco, and β-manno configurations, respectively. 5a-Carba sugar analog 2 of biologically interesting disaccharide β-D-GlcpNAc-(14)-D-Manp (1) was synthesized.

Methyl 5a′-carbamaltoses linked by imino, ether, and sulfide bridges were synthesized by coupling of an amino carbasugar with a sugar epoxide and of the carbasugar epoxide with the oxide anion or thioacetate derived from sugar derivatives. Their unsaturated derivatives related to a potent α-glucosidase inhibitor, methyl acarviosin, were also synthesized. Moderate inhibitory activity against baker's yeast α-glucosidase was observed only for the imino-linked compounds 2 and 5.

Four configurational types of two protected O‐linked (5a‐carba‐D‐hexopyranosyl)‐D‐glucal and carba‐D‐glucal derivatives were prepared in order to provide versatile synthetic intermediates readily convertible into carba‐oligosaccharides of biological interest. These compounds may also find application as donors for elongation of carba‐oligosaccharide chains having O‐linked carbahexopyranose residues at nonreducing ends.

The spiro‐epoxide derived from (−)‐2‐deoxy‐scyllo‐inosose was converted into the iodide 2, which was directly subjected to elimination conditions, affording the key methylene compound 4. Successive cyclohexylidenation of the tetrol obtained from 4, selective benzoylation, and conventional tosylation gave the homoallyl tosylate 11, which would be a versatile intermediate for preparation of biologically active 5a‐carbahexopyranosylamines and their unsaturated congeners.

Demethylthio-, S-demethyl-, and S-ethyl derivatives of the α-mannosidase inhibitor, mannostasin A, were synthesized and evaluated for their inhibition of Jack bean α-mannosidase with the prime objective of elucidating the role of the methylthio group. All methylthio derivatives had significantly lowered inhibitory potentials. However, one mannostatin A analogue with a methoxyl instead of the methylthio group exhibited about twofold enhancement of the activity. The structure and inhibitory activity relationships of mannostatin A and related compounds are discussed in light of our results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

In continuation of development of bioactive inositol derivatives, a 1-O-methyl derivative of 5-amino-5-deoxy-L-talo-quercitol was designed and synthesized as an analogue of the strong alpha-fucosidase inhibitor, 5a-carba-alpha-L-fucopyranosylamine, the methyl branch being replaced with methoxyl, and demonstrated to be a moderate alpha-fucosidase inhibitor. The present approach provides a possible route to apply alkyl ethers of aminodeoxyinositols as hexopyranose mimics of biological interest.

In the course of chemical modification of alpha-fucosidase inhibitors of 5a-carba-fucopyranosylamine type, an N-dodecyl derivative of the enantiomer 6-deoxy-5a-carba-beta-D-galactopyranosylamine demonstrated very strong inhibition of beta-galactosidase and beta-glucosidase. This finding led us to synthesize corresponding 6-hydroxy compounds, in order to elucidate structure-activity relationships for inhibitors of this type. Among four N-alkyl-5a-carba-beta-D-galactopyranosylamines prepared, the N-octyl derivative could be demonstrated to possess moderate activity toward alpha- and beta-galactosidases, and beta-glucosidase.

Since glycosidase and glycosyltransferase inhibitors, composed of carba-sugars, have recently attracted much attention, it is desirable to develop effective preparative routes for provision of new carba-sugar derivatives of potential biological interest. 1,2:3,6-Dianhydro-5a-carba-alpha-glucopyranose was here chosen for study of synthetic utility, and demonstrated to be a promising intermediate for supplying several carba-beta-glycosylamines and N-linked dicarba-oligosaccharides. An N-linked 5a,5a'-dicarbalactose derivative obtained here was found to be a strong alpha-galactosidase inhibitor (IC50 1.2 microM, green coffee beans).

Valienamine analogues having alpha- and beta-galactose-type structures were synthesized by racemic modification from (1SR,2RS,3SR)-6-methylenecyclohex-4-ene-1,2,3-triol. Four N-alkyl derivatives of the beta-anomer were readily prepared selectively by treatment of key intermediate 2,6-di-O-acetyl-3,4-O-isopropylidene-5a-carba-alpha- and beta-l-arabino-hex-5(5a)-enopyranosyl bromides with alkyl amines. All compounds were assayed for inhibitory activity against six glycosidases, and the N-dodecyl derivative was shown to be a very strong inhibitor of beta-galactosidase (IC(50) 0.01 microM, bovine liver).

カルバ糖質は真糖の炭素環状アナログであり、最近、糖鎖生化学、糖鎖生物学の分野において注目される一群の擬似糖質に属している。カルバ糖の化学構造は、ピラノース環を有する五単糖、六単糖のそれらに酷似するが、分子中にアルデヒド基あるいはケトン基が存在しないので、生体内における安定性や反応性については、還元糖と大きな違いを見せている。とくにカルバ糖アミンは、天然から得られたもの、それを参考にして合成されたもの、いずれもが、真のグリコシルアミン類に期待される性状に、化学的安定性を賦与した格好なミミックスとして興味深い生理活性を示すことが分かってきた。さらに、グリコシダーゼによって加水分解されない、N-あるいはO-結合型オリゴ糖残基を含むオリゴ糖ミミックスの設計と合成が容易に行えるようになり、それらの興味深い性質が明らかにされつつある。カルバ糖の化学は、今後、生理活性糖ミミックスや糖鎖生物学・生化学研究のツールなどの開発現場で重要な位置を占めることが予期される。

Convenient and practical synthesis of (+)-valiolamine and (-)-1-epi-valiolamine from (-)-vibo-quercitol, 1-deoxy-L-myo-inositol, readily obtained by bioconversion of myo-inositol, is described.

We synthesized a galactose derivative, N- octyl-4-epi-β-valienamine (NOEV), for a molecular therapy (chemical chaperone therapy) of a human neurogenetic disease, β-galactosidosis (G M1 -gangliosidosis and Morquio B disease). It is a potent inhibitor of lysosomal β-galactosidase in vitro . Addition of NOEV in the culture medium restored mutant enzyme activity in cultured human or murine fibroblasts at low intracellular concentrations, resulting in a marked decrease of intracellular substrate storage. Short-term oral administration of NOEV to a model mouse of juvenile G M1 -gangliosidosis, expressing a mutant enzyme protein R201C, resulted in significant enhancement of the enzyme activity in the brain and other tissues. Immunohistochemical stain revealed a decrease in the amount of G M1 and G A1 in neuronal cells in the fronto-temporal cerebral cortex and brainstem. However, mass biochemical analysis did not show the substrate reduction observed histochemically in these limited areas in the brain probably because of the brief duration of this investigation. Chemical chaperone therapy may be useful for certain patients with β-galactosidosis and potentially other lysosomal storage diseases with central nervous system involvement.

For the purpose of providing biologically stable building blocks for the biocombinatorial synthesis using a living cell, some ether-linked alkyl 5a-carba-beta-D-glycoside primers were prepared. The key step of the synthesis was coupling of 1-bromo-n-alkanes with the 1-OH unprotected derivatives of 5a-carba-sugar analogues of D-glucose, D-galactose, and 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), in DMF in the presence of sodium hydride. Alternatively, alkyl carba-lactoside was synthesized by incorporation of a 5a-carba-beta-D-galactose residue into the 4-position of dodecyl beta-D-glucopyranoside. A strong and specific inhibition of beta-galactosidase (K(i) 0.67 microM, bovine liver) was found for dodecyl 5a-carba-beta-D-galactopyranoside.

N-Octyl-beta-valienemine (1), a potent beta-glucocerebrosidase inhibitor, was chemically transformed into two biologically interesting compounds: the 4-epimer, beta-galacto-type N-octyl-valienamine, and the 4-O-(beta-D-galactopyranosyl) derivative, a carba-lactosylceramide analogue. The former, interestingly, could be demonstrated to act as a very effective inhibitor (IC(50)=0.3 microM) of human beta-galactosidase. The latter exhibited moderate inhibitory activity (IC(50)=20 microM) against beta-glucocerebrosidase (mouse liver).

Discovery of a very potent α-fucosidase inhibitor 5a-carba-α- l -fucopyranosylamine ( 1 ) led to preparation of its β-anomer Figure 1 , Scheme 1 and the respective unsaturated derivatives, fucose-type α- and β-valienamines ( Figure 1 , Scheme 2 and Figure 1 , Scheme 2 ), in order to elucidate the structure–activity relationship of carba-aminosugar inhibitors of this kind. Compound Figure 1 , Scheme 1 was demonstrated to be a potent inhibitor (Ki=2.0 × 10−7 M, bovine kidney), possessing ca. one-tenth of the activity of the parent 1 . Interestingly, Figure 1 , Scheme 2 and Figure 1 , Scheme 2 were found to be rather weak inhibitors, contrary to the expectations based on the activity relationships between the α-glucosidase inhibitors, α-glucose-type validamine and valienamine.

5a-Carba-α-L-fucopyranosylamine (5), an α-glucosidase inhibitor validamine analog possessing an α-L-fucose-type structure, and four related compounds (4 and 6−8) were synthesized and their glycosidase inhibitory potential determined. Carbafucosylamine has already been shown to possess a specific and very strong inhibitory activity against α-L-fucosidase (Ki = 1.2 × 10−8M, bovine kidney). Judging from the activity of the other analogs prepared, this amine might be expected to be a lead compound for development of a new type of α-L-fucosidase inhibitor.

Oxidation of three di-O-isopropylidene derivatives 2a—4a, newly derived from (+)-epi-quercitol (1), with acetic anhydride in DMSO gave the corresponding ketones 5—7, which underwent aldol-type condensation with nitromethane under basic conditions to give selectively the protected derivatives 8a—10a of C-nitromethyl-1,2,3,4,5-cyclohexanepentols, respectively. On treatment with diazomethane in DMSO, the ketones 6 and 7 gave single spiro epoxides 11 and 12, the structures of which were confirmed by converting them into new C-(azidomethyl)cyclohexanepentols 16 and 17. The nitro compounds were hydrogenated in the presence of Raney nickel to give the amines isolated as the N-acetyl derivatives. Deprotection gave three new 1- and 3-C-aminomethyldeoxyinositols 15c—17c. The aminocyclitols obtained and their N-acetyl derivatives were assayed for inhibitory activity against examples of glycosidases.

5a-Carba-α-DL-fucopyranosylamine (DL-5) and -galactopyranosylamine (DL-4) have been synthesized in a conventional manner from 2,3,4,6-tetra-O-acetyl-5a-carba-β-DL-glucopyranosyl bromide (6). Only compound DL-5 has been shown to be a strong inhibitor (Ki = 2.3 × 10−7M) of α-fucosidase (bovine kidney). They did not exhibit any inhibitory activity towards five glycoside hydrolases, namely α- and β-glucosidases and α- and β-galactosidases.

glycosidic linkages.In fact, the C2S bond length (1.78 A˚ ) and C2S2C bondangle (99°) strongly differ from the values for C2O (1.41A˚ ) and C2O2C (116°). On the other hand, the C2N dis-tance and C2N2C bond angle values are 1.47 A˚ and be-tween 116.52119.6°, according to MM3* calculations. Onthis basis, we report here the conformational study of thethioglycoside- (

Twelve 1,2- and 2,3-anhydro-1,2,3,4,5-cyclohexanepentols were synthesized from (+)-epi- and (-)-vibo-quercitols, readily available by bioconversion of myo-inositol, and assayed for inhibitory activity against glucocerebrosidase (mouse liver). Among them 1L-1,2-anhydro-1,2,4/3,5-cyclohexanepentol, the 3-deoxy derivative of the irreversible inhibitor conduritol B epoxide (CBE), has been demonstrated to be a highly potent and specific inhibitor, almost comparable to the parent compound.

Synthesis of ether-linked octyl 5a′-carba-β-lactosaminide 3 and -isolactosaminide 5 was carried out in seven steps, starting from the coupling products of 1,2-anhydro-5a-carba-β-D-mannopyranose derivative 7, and the oxide anions generated from the octyl N-acetyl-β-D-glucosaminide derivatives 13 and 16, respectively, under basic conditions. The 5a-carba-α-D-mannopyranose residues of the coupling products 17 and 26 were transformed into the β-D-gluco configuration through epimerization of the respective 2′-oxo derivatives 19 and 28, and selective reduction, and then into the β-D-galacto configuration by direct nucleophilic substitution of their 4′,6′-dimesylates 23 and 31 with an acetate ion. Biological assay has shown that 3 is an acceptor substrate for human-milk α-(13/4)-fucosyltransferase and, interestingly, 5 is not. In addition, the imino-linked congeners 4 and 6 have been synthesized by coupling of the 4-amino-4-deoxy- and 3-amino-3-deoxy derivatives 37 and 41 of octyl N-acetyl-β-D-glucosaminide, and the carba-sugar epoxide 8, respectively, and subsequent deprotection. Compound 4 is a substrate while 6 is neither a substrate nor an inhibitor for fucosyltransferase. Small-scale enzymatic synthesis was carried out by treatment of 3 and 4 with GDP-fucose and milk fucosyltransferase, which resulted in conversion into the corresponding trisaccharides 47 and 48, respectively.

The chiral total synthesis of paniculide A ( 1 ), a highly oxygenated sesquiterpene possessing a bisabolane skeleton, starting from D-glucose is described. The two different approaches, both involved Ferrier's carbocyclization reaction to construct the cyclohexane unit in 1 , were explored. The first approach, employing the carbocyclization of bicyclic substrate furnished the formal total synthesis. The second approach, designed to suppress the undesired side reactions observed in the first one, adopted the carbocyclization of a monocyclic substrate, and Claisen rearrangement for the stereoselective carbon-carbon bond formation. The successful total synthesis of 1 revealed the effectiveness of the combination of Ferrier's carbocyclization and Claisen rearrangement for the chiral synthesis of highly oxygenated natural products possessing cyclohexane units.

Two kojibiose-type pseudo-disaccharides and a trisaccharide, containing a 5-amino-1,2,3,4-cyclopentanetetrol derivative or valienamine, linked by way of nitrogen bridges to the sugar residues, have been designed and synthesized as processing alpha-glucosidase I inhibitors. Synthesis of the pseudo-disaccharides was carried out starting from the coupling products of the sugar isothiocyanates and an aminocyclitol, respectively, by cyclization with mercury(II) oxide to the cyclic isoureas and subsequent deprotection. Pseudokojibiose was prepared in a poor yield by reaction of a protected valienamine and a sugar epoxide, followed by deprotection. Although the pseudooligosaccharides are all strong inhibitors of alpha-glucosidase (baker's yeast), they did not have any inhibitory potency against either sucrase isomaltase (rat intestine) or processing alpha-glucosidase (rat liver microsomes).

The chiral and stereoselective total synthesis of novel cerebrosides, acanthacerebroside A (1) and astrocerebroside A (2), isolated from starfish, is described. The phytosphingosine moieties in 1 and 2 were prepared by the coupling reaction of dialkylmagnesium reagents with the common epoxide intermediate, 2-(t-butoxycarbonyl)amino-1-O-(t-butyldiphenylsilyl)-2-deoxy-3-O-(4-methoxybenzyl)-D-4,5-anhydroribitol (5). The epoxide (5) was synthesized from naturally occurring cyclitol, L-quebrachitol via the conduramine derivative, which was prepared regio- and stereoselectively by the Pd-catalyzed azidation of the allyl carbonate derivative. Condensation of phytosphingosines with 2-acetoxy fatty acid residue, followed by glycosidation, furnished the total synthesis. This work established an effective synthetic pathway to a wide variety of cerebrosides containing various phytosphingosines and 2-hydroxy fatty acid residue; the first total synthesis of astrocerebroside A (2) fully confirmed the proposed structure.

The chiral and stereoselective synthesis of (+)-lactacystin 1, the first non-protein neurotrophic factor having an α,α-disubstituted α-amino acid structure, is described. The highly functionalized γ-lactam portion possessing a tetra-substituted carbon with nitrogen in 1 was effectively constructed from d-glucose using allylic trichloroacetimidate rearrangement (Overman rearrangement) as the key reaction.

All stereoisomers with regard to C-1 and 2 of 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) analogue containing unsaturated (β-valienamine) and saturated 5a-carba-β- d -glucopyranosylamine (β-validamine) residues in place of morpholine moiety were synthesized. Although PDMP is a potent and specific glucosylceramide synthase inhibitor, the former valienamine analogues (4a-d) have been shown to be strong glucocerebrosidase inhibitors ( IC 50 3–7 ∗x 10 −7 M). The latter validamine analogues (5a-d) were also moderate glucocerebrosidase inhibitors ( IC 50 5–20 ∗x 10 −6 M). A series of compounds synthesized lacked an inhibitory potency against the glucosyltransferase at all. Whereas the analogue 6a composed of epimeric α-valienamine residue did not possess any potency against both enzymes.

Twenty-four stereoisomers of 5-amino- and 5-amino-C-(hydroxymethyl)-1,2,3,4-cyclopentanetetraols and twenty-six of the corresponding N-phenyl cyclic isourea derivatives were assayed for inhibitory activity against six glycosidases. Among them, as has been expected for structure mimics of putative transition state glucopyranosyl cation for glycoside hydrolysis, 1 l -(1,2,4, 5 3 )-5-amino -1-C- (hydroxymethyl)-1,2,3,4-cyclopentanetetraol l -4 and its N-phenyl cyclic isourea derivative S-19 were shown to have strong inhibitory activity, IC50 4 × 10−7 and 7.6 × 10−9 M, respectively, against baker's yeast α-glucosidase. It has been analogously explained that compounds R,S-22 and R,S-26 possessed high inhibitory potency against Escherichia coli and bovine liver β-galactosidases, respectively.

A chiral synthesis of the Sceletium alkaloid (-)-mesembranol 1 is described. The cyclohexane ring in 1 is prepared in an optically active form from D-glucose using Ferrier’s carbocyclisation, and the critical stereochemistry of the quaternary carbon in 1 is constructed stereoselectively via chirality transfer by way of Claisen rearrangement of the cyclohexenol derivative 14a. The perhydroindole skeleton in 1 is effectively generated by intramolecular aminomercuriation of the amino-olefin 18.

The thermal intramolecular Diels–Alder cycloaddition of a 2 : 1 mixture of ethyl (2E,8E and Z, 10E,13R)-13-(t-butyldimethylsilyl) oxy-2,10-dimethyl-2,8,10-pentadecatrienoate provided four diastereomeric cycloadducts. Deprotection of one of the cycloadducts provided PI-201, a novel platelet aggregation inhibitor, as its natural form. Three stereoisomers of PI-201 were prepared from the other cycloadducts. The intramolecular cycloadditions of some structurally similar trienes were also investigated.

Six homologous derivatives (N-butyl3a, hexyl 3b, octyl 3c, decyl 3d, tetradecyl 3e and stearyl 3f) of β-valienamine were synthesized. All have been shown to be potent and specific inhibitors of β-glucocerebrosidase, and to have no potency against glucosylceramide synthase (mouse liver microsomes). Among them, the N-octyl derivative possesses the strongest activity (IC50 3 × 10−8 M), being almost 10-fold more potent compared to the unsaturated 5a-carba-glucosylceramide 1. Compounds 3b and 3c are also moderate inhibitors of α-glucosidase (Baker's yeast).