Intermolecular Michael addition of substituted amines to a sugar-derived alpha,beta-unsaturated ester: synthesis of 1-deoxy-D-gluco- and -L-ido-homonojirimycin, 1-deoxy-castanospermine and 1-deoxy-8a-epi-castanospermine

D-Glucose-Derived 1,2,4-Trioxepanes: Synthesis, Conformational Study, and Antimalarial Activity

New enantiomerically pure 1,2,4-trioxepanes 10a,b/11a,b were synthesized from D-glucose. Their conformational behavior was studied by low-temperature NMR and substantiated by DFT calculations. On evaluation of in vitro antimalarial activity, the adamantyl derivative 11b showed IC50 values in the low micromolar range, particularly against the W2 chloroquine-resistant Plasmodium falciparum strain (IC50 = 0.15 ± 0.12 μM).

Enantioselective synthesis of polyhydroxyindolizidinone and quinolizidinone derivatives from a common precursor

A concise asymmetric synthetic route to two new tetrahydroxyindolizidinone and quinolizidinone derivatives has been developed from a common intermediate which featured a highly selective dihydroxylation reaction and a RCM reaction as key steps.

Divergent total synthesis of 1,6,8a-tri-epi-castanospermine and 1-deoxy-6,8a-di-epi-castanospermine from substituted azetidin-2-one (β-lactam), involving a cascade sequence of reactions as a key step

A divergent, short, and novel total synthesis of 1,6,8a-tri-epi-castanospermine (7) and 1-deoxy-6,8a-di-epi-castanospermine (8) has been developed via a common precursor, 15, obtained from D-mannitol derived β-lactam. The key step involves a one pot cascade sequence of trimethyl sulfoxonium ylide based cyclization of epoxy sulfonamide 14via epoxide ring opening, one carbon homologation followed by intramolecular cyclization.

Molecular architecture with carbohydrate functionalized β-peptides adopting 314-helical conformation

Carbohydrate recognition is essential in cellular interactions and biological processes. It is characterized by structural diversity, multivalency and cooperative effects. To evaluate carbohydrate interaction and recognition, the structurally defined attachment of sugar units to a rigid template is highly desired. β-Peptide helices offer conformationally stable templates for the linear presentation of sugar units in defined distances. The synthesis and β-peptide incorporation of sugar-β-amino acids are described providing the saccharide units as amino acid side chain. The respective sugar-β-amino acids are accessible by Michael addition of ammonia to sugar units derivatized as α,β-unsaturated esters. Three sugar units were incorporated in β-peptide oligomers varying the sugar (glucose, galactose, xylose) and sugar protecting groups. The influence of sugar units and the configuration of sugar-β-amino acids on β-peptide secondary structure were investigated by CD spectroscopy.

Chromium-mediated stereoselective synthesis of carbohydrate-derived (E)-α,β-unsaturated esters or amides

A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results.

Highly regio- and stereoselective one-pot synthesis of carbohydrate-based butyrolactones

The use of manganese(III) acetate allows the direct synthesis of diverse arrays of [4.3.0] bicyclic carbohydrate-based γ-lactone building blocks from glycals. A mechanism to explain the high regio- and stereoselectivity is proposed. The new reaction has the potential to generate libraries for biological screening.

Synthesis, computational study and glycosidase inhibitory activity of polyhydroxylated conidine alkaloids--a bicyclic iminosugar

New bicyclic conidine iminosugars 1d and 1e were synthesized from D-glucose. Thus, D-glucose was converted to sugar beta-amino acids 3a and 3b in good yields. Individual treatment of 3a/3b with the Mukaiyama reagent afforded sugar beta-lactams 4a/4b that on reduction with LiAlH(4)/AlCl(3) gave azetidines 5a/5b with a sugar appendage. Reductive aminocyclization of sugar azetidines 5a/5b afforded the corresponding conidine iminosugars 1d/1e. Based on the (1)H NMR and DFT calculation studies the conformation of 1d was assigned as half chair A2 and that of 1e as a boat B2. The glycosidase inhibitory activities of 1d and 1e such as alpha-mannosidase, alpha-glucosidase and alpha-galactosidase were studied. The alpha-amylase activity was compared with acarbose. Compound 1d was found to be a moderate inhibitor of glycosidases while 1e was noticed to be a good inhibitor of alpha-mannosidase and a moderate inhibitor of other glycosidases. These results were substantiated by molecular docking studies using WHAT IF software and the AUTODOCK 3.0 program.

Convergent Approach toward the Synthesis of the Stereoisomers of C-6 Homologues of 1-Deoxynojirimycin and Their Analogues: Evaluation as Specific Glycosidase Inhibitors

A new and stereoselective strategy is developed to synthesize an appropriate template 9 to obtain C-6 homologues of 1-deoxyazasugars such as 1-deoxy-D-galactohomonojirimycin (5), 1-deoxy-4-hydroxymethyl-D-glucohomonojirimycin (6), and their enantiomers. The template 9 is also used to obtain neutral nonbasic pseudo-glyconolactam (8), C-4 amino, and methyl analogues of 1-deoxy-homonojirimycin as new analogues of 1-deoxyhomoazasugars. Compound 5 is found to be a potent and specific inhibitor to alpha-galactosidase (Ki = 1.7 microM). Similarly compounds 6 (Ki= 28 microM), ent-5 (Ki= 129 microM), and ent-6 (Ki= 12 microM) exhibited specific inhibition of beta-glucosidase.

Polyhydroxylated homoazepanes and 1-deoxy-homonojirimycin analogues: Synthesis and glycosidase inhibition study

The Johnson-Claisen rearrangement of D-gluco and L-ido-derived allylic orthoesters afforded gamma,delta-unsaturated ester that on ester reduction, epoxidation, regioselective oxirane opening by sodium azide and hydrogenation led to sugar amino alcohols--immediate precursors for 1-deoxy-homonojirimycin 3a,b, and polyhydroxylated homoazepanes 4a,b. Our synthetic approach and glycosidase inhibitory activity is reported.

Synthesis of Pentahydroxy Indolizidine Alkaloids Using Ring Closing Metathesis: Attempts To Find the Correct Structure of Uniflorine A

Ring closing metathesis of d-glucose derived diene-substrate containing nitrogen functionality followed by asymmetric dihydroxylation afforded sugar substituted dihydroxylated pyrrolidines 8a-c which on 1,2-acetonide deprotection and reductive amination afforded putative uniflorine A 2a and its analogues 2b-c, respectively.

Intramolecular 5-endo-Trig Aminomercuration of β-Hydroxy-γ-alkenylamines: Efficient Route to a Pyrrolidine Ring and Its Application for the Synthesis of (+)-Castanospermine and Analogues

The intramolecular aminomercuration reaction of sugar-derived beta-hydroxy-gamma-alkenylamines 8a-c undergoes 5-endo-trig cyclization in high yield. The sugar-substituted pyrrolidines thus obtained were elaborated to the synthesis of polyhydroxylated indolizidine alkaloids, namely, castanospermine 1a, 1-epi-castanospermine 1b, and 8a-epi-castanospermine 1c, having promising glycosidase inhibitory activities.

Synthesis and evaluation of glycosidase inhibitory activity of N-butyl 1-deoxy-D-gluco-homonojirimycin and N-butyl 1-deoxy-L-ido-homonojirimycin

Conjugate addition of n-butyl amine to d-glucose derived alpha,beta-unsaturated ester 4 afforded beta-amino esters 5a,b that on reduction of ester group, 1,2-acetonide deprotection, and reductive amination led to the formation of corresponding N-butyl 1-deoxy-D-gluco-homonojirimycin 2c and N-butyl 1-deoxy-L-ido-homonojirimycin 2d which were found to be selective beta-glucosidase inhibitors with an IC(50) value in millimolar range.

An expeditious stereoselective synthesis of natural (−)-Cassine via cascade HWE [3 + 2]-cycloaddition process

l-Rhamnose is transformed to (-)-Cassine via a remarkable four step one pot reaction. The Horner-Wadsworth-Emmons [3 + 2]-1,3-dipolar cycloaddition reaction cascade is the pivotal step in this reaction sequence and makes the synthesis highly efficient.

Synthesis of tetrahydroxy perhydroaza-azulenes: tandem Johnson–Claisen rearrangement ofd-glucose-derived allylic alcohols

The Johnson-Claisen rearrangement of D-glucose-derived allylic alcohols 5a,b, afforded sugar-substituted gamma,delta-unsaturated ester in high yield. Conversion of the ester group to an azidomethyl group, epoxidation of the double bond and hydrogenation gave pyrrolidine ring skeletons 13a and 13b, which were transformed to tetrahydroxy perhydroaza-azulenes 1a and 1b, respectively. Glycosidase inhibitory activity was also evaluated.

The 5-endo-trig cyclization of D-glucose derived gamma-alkenylamines with mercury (II) salts: synthesis of 1-deoxycastanospermine and its 8a-epi-analogue

The intramolecular aminomercuration of gamma-alkenylamines 1a, 1b and 4 was shown to afford the 5-endo-trig cyclized product exclusively in good yield. The utility of pyrrolidine derivatives thus obtained from D-glucose derived gamma-alkenylamines 1a and 1b was demonstrated in the synthesis of 1-deoxycastanospermine (3a) and 1-deoxy-8a-epi- castanospermine (3b).

1,3-Dipolar Cycloaddition Reaction of d-Glucose-Derived Nitrone with Allyl Alcohol: Synthesis of 2-Hydroxy-1-deoxycastanospermine Analogues

[reaction: see text] The synthesis and evaluation of glycosidase inhibitory activity of polyhydroxylated indolizidine alkaloids namely 2-hydroxy-1-deoxycastanospermine 3a,b and 2-hydroxy-1-deoxy-8a-epi-castanospermine 3c,d is reported. The key step involves the intermolecular 1,3-dipolar cycloaddition of allyl alcohol to d-glucose-derived nitrone 4, followed by tosylation, that afforded four diastereomeric sugar-substituted isoxazolidines 5a-d with the desired regioselectivity. The one-pot conversion of 5a-d to pyrrolidines 8a-d by hydrogenolysis, removal of 1,2-acetonoide functionality, and hydrogenation afforded corresponding target molecules 3a-d.

Synthesis and evaluation of the glycosidase inhibitory activity of 5-hydroxy substituted isofagomine analogues

An efficient strategy for the synthesis of 5-hydroxy substituted isofagomine analogues and , having both -CH2OH/CH3 and -OH functionality at the C-5 position, and evaluation of their inhibitory potency is reported. The synthetic methodology involves the aldol-Cannizzaro reaction of easily available alpha-d-xylopentodialdose followed by hydrogenolysis to afford the triol . Selective amidation of the alpha- and beta-hydroxymethyl group at C-4, deprotection of the 1,2-acetonide group and hydrogenation gave the target molecules, which were found to be potent against beta-glycosidases with IC50 values in the micro molar range. Compound showed excellent potency against glycosidases and human salivary amylase.

Aziridine carboxylate from d-glucose: synthesis of polyhydroxylated piperidine, pyrrolidine alkaloids and study of their glycosidase inhibition

The D-glucose derived aziridine carboxylate 5 was obtained from (E)-ethyl-6-bromo-1,2-O-isopropylidene-3-O-benzyl-5-deoxy-alpha-D-xylo-5-eno-heptofuranuronate 4 through conjugate addition of benzylamine and in situ intramolecular nucleophilic expulsion of bromine. The regioselective aziridine ring-opening, using water as a nucleophile, resulted in the alpha-hydroxy-beta-aminoester 6, which was exploited in the synthesis of six and five membered azasugars 1b/1c and 2b/2c, respectively. The glycosidase inhibitory activity of the title compounds was evaluated.