Isolation from Stevia rebaudiana of DMDP acetic acid, a novel iminosugar amino acid: synthesis and glycosidase inhibition profile of glycine and ß-alanine pyrrolidine amino acids.

DMDP acetic acid [N-carboxymethyl-2,5-dideoxy-2,5-imino-D-mannitol] 5 from Stevia rebaudiana is the first isolated natural amino acid derived from iminosugars bearing an N-alkyl acid side chain; it is clear from GCMS studies that such derivatives with acetic and propionic acids are common in a broad range of plants including mulberry, Baphia, and English bluebells, but that they are very difficult to purify. Reaction of unprotected pyrrolidine iminosugars with aqueous glyoxal gives the corresponding N-acetic acids in very high yield; Michael addition of both pyrrolidine and piperidine iminosugars and that of polyhydroxylated prolines to tert-butyl acrylate give the corresponding N-propionic acids in which the amino group of ß-alanine is incorporated into the heterocyclic ring. These easy syntheses allow the identification of this new class of amino acid in plant extracts and provide pure samples for biological evaluation. DMDP N-acetic and propionic acids are potent α-galactosidase inhibitors in contrast to potent ß-galactosidase inhibition by DMDP.

d-Idose, d-Iduronic Acid, and d-Idonic Acid from d-Glucose via Seven-Carbon Sugars.

A practical synthesis of the very rare sugar d-idose and the stable building blocks for d-idose, d-iduronic, and d-idonic acids from ido-heptonic acid requires only isopropylidene protection, Shing silica gel-supported periodate cleavage of the C6-C7 bond of the heptonic acid, and selective reduction of C1 and/or C6. d-Idose is the most unstable of all the aldohexoses and a stable precursor which be stored and then converted under very mild conditions into d-idose is easily prepared.

In silico analyses of essential interactions of iminosugars with the Hex A active site and evaluation of their pharmacological chaperone effects for Tay-Sachs disease.

The affinity of a series of iminosugar-based inhibitors exhibiting various ring sizes toward Hex A and their essential interactions with the enzyme active site were investigated. All the Hex A-inhibiting iminosugars tested formed hydrogen bonds with Arg178, Asp322, Tyr421 and Glu462 and had the favorable cation-π interaction with Trp460. Among them, DMDP amide (6) proved to be the most potent competitive inhibitor with a Ki value of 0.041 µM. We analyzed the dynamic properties of both DMDP amide (6) and DNJNAc (1) in aqueous solution using molecular dynamics (MD) calculations; the distance of the interaction between Asp322 and 3-OH and Glu323 and 6-OH was important for stable interactions with Hex A, reducing fluctuations in the plasticity of the active site. DMDP amide (6) dose-dependently increased intracellular Hex A activity in the G269S mutant cells and restored Hex A activity up to approximately 43% of the wild type level; this effect clearly exceeded the border line treatment for Tay-Sachs disease, which is regarded as 10-15% of the wild type level. This is a significantly greater effect than that of pyrimethamine, which is currently in Phase 2 clinical trials. DMDP amide (6), therefore, represents a new promising pharmacological chaperone candidate for the treatment of Tay-Sachs disease.

6-Deoxyhexoses from l-Rhamnose in the Search for Inducers of the Rhamnose Operon: Synergy of Chemistry and Biotechnology.

In the search for alternative non-metabolizable inducers in the l-rhamnose promoter system, the synthesis of fifteen 6-deoxyhexoses from l-rhamnose demonstrates the value of synergy between biotechnology and chemistry. The readily available 2,3-acetonide of rhamnonolactone allows inversion of configuration at C4 and/or C5 of rhamnose to give 6-deoxy-d-allose, 6-deoxy-d-gulose and 6-deoxy-l-talose. Highly crystalline 3,5-benzylidene rhamnonolactone gives easy access to l-quinovose (6-deoxy-l-glucose), l-olivose and rhamnose analogue with C2 azido, amino and acetamido substituents. Electrophilic fluorination of rhamnal gives a mixture of 2-deoxy-2-fluoro-l-rhamnose and 2-deoxy-2-fluoro-l-quinovose. Biotechnology provides access to 6-deoxy-l-altrose and 1-deoxy-l-fructose.

3-Fluoroazetidinecarboxylic Acids and trans,trans-3,4-Difluoroproline as Peptide Scaffolds: Inhibition of Pancreatic Cancer Cell Growth by a Fluoroazetidine Iminosugar.

Reverse aldol opening renders amides of 3-hydroxyazetidinecarboxylic acids (3-OH-Aze) unstable above pH 8. Aze, found in sugar beet, is mis-incorporated for proline in peptides in humans and is associated with multiple sclerosis and teratogenesis. Aze-containing peptides may be oxygenated by prolyl hydroxylases resulting in potential damage of the protein by a reverse aldol of the hydroxyazetidine; this, rather than changes in conformation, may account for the deleterious effects of Aze. This paper describes the synthesis of 3-fluoro-Aze amino acids as hydroxy-Aze analogues which are not susceptible to aldol cleavage. 4-(Azidomethyl)-3-fluoro-Aze and 3,4-difluoroproline are new peptide building blocks. trans,trans-2,4-Dihydroxy-3-fluoroazetidine, an iminosugar, inhibits the growth of pancreatic cancer cells to a similar degree as gemcitabine.

Nine of 16 stereoisomeric polyhydroxylated proline amides are potent ß-N-acetylhexosaminidase inhibitors.

All 16 stereoisomeric N-methyl 5-(hydroxymethyl)-3,4-dihydroxyproline amides have been synthesized from lactones accessible from the enantiomers of glucuronolactone. Nine stereoisomers, including all eight with a (3R)-hydroxyl configuration, are low to submicromolar inhibitors of ß-N-acetylhexosaminidases. A structural correlation between the proline amides is found with the ADMDP-acetamide analogues bearing an acetamidomethylpyrrolidine motif. The proline amides are generally more potent than their ADMDP-acetamide equivalents. ß-N-Acetylhexosaminidase inhibition by an azetidine ADMDP-acetamide analogue is compared to an azetidine carboxylic acid amide. None of the amides are good α-N-acetylgalactosaminidase inhibitors.

Short and sweet: (D)-glucose to (L)-glucose and (L)-glucuronic acid.

The scarcity and expense of access to L-sugars and other rare sugars have prevented the exploitation of their biological potential; for example D-psicose, only recently available, has been recognized as an important new food. Here we give the definitive and cheap synthesis of 99.4% pure L-glucose from D-glucose which requires purification of neither intermediates nor final product other than extraction into and removal of solvents; a simple crystallization will raise the purity to >99.8%.

C-branched iminosugars: α-glucosidase inhibition by enantiomers of isoDMDP, isoDGDP, and isoDAB-L-isoDMDP compared to miglitol and miglustat.

The Ho crossed aldol condensation provides access to a series of carbon branched iminosugars as exemplified by the synthesis of enantiomeric pairs of isoDMDP, isoDGDP, and isoDAB, allowing comparison of their biological activities with three linear isomeric natural products DMDP, DGDP, and DAB and their enantiomers. L-IsoDMDP [(2S,3S,4R)-2,4-bis(hydroxymethyl)pyrrolidine-3,4-diol], prepared in 11 steps in an overall yield of 45% from d-lyxonolactone, is a potent specific competitive inhibitor of gut disaccharidases [K(i) 0.081 µM for rat intestinal maltase] and is more effective in the suppression of hyperglycaemia in a maltose loading test than miglitol, a drug presently used in the treatment of late onset diabetes. The partial rescue of the defective F508del-CFTR function in CF-KM4 cells by L-isoDMDP is compared with miglustat and isoLAB in an approach to the treatment of cystic fibrosis.

An approach to 8 stereoisomers of homonojirimycin from (D)-glucose via kinetic & thermodynamic azido-γ-lactones.

Crystal structures were obtained for the two C2 epimeric azido-γ-lactones 2-azido-2-deoxy-3,5:6,7-di-O-isopropylidene-d-glycero-d-ido-heptono-1,4-lactone and 2-azido-2-deoxy-3,5:6,7-di-O-isopropylidene-d-glycero-d-gulo-heptono-1,4-lactone prepared from kinetic and thermodynamic azide displacements of a triflate derived from d-glucoheptonolactone. Azido-γ-lactones are very useful intermediates in the synthesis of iminosugars and polyhydroxylated amino acids. In this study two epimeric azido-heptitols allow biotechnological transformations via Izumoring techniques to 8 of the 16 possible homonojirimycin analogues, 5 of which were isolated pure because of the lack of stereoselectivity of the final reductive amination. A side-by-side glycosidase inhibition profile of 11 of the possible 16 HNJ stereoisomers derived from d-glucose and d-mannose is presented.

(3R,4S,5R,6R,7S)-3,4,5,7-Tetrahydroxyconidine, an azetidine analogue of 6,7-diepicastanospermine and a conformationally constrained d-deoxyaltronojirimycin, from l-arabinose.

The synthesis from l-arabinose of an azetidine analogue of 6,7-diepicastanospermine and its glycosidase inhibition profile are described.

2-N-Benzyl-2,6-dide-oxy-2,6-imino-3,4-O-iso-propyl-idene-d-allono-nitrile.

X-ray crystallography firmly established the relative stereochemistry of the title compound, C16H20N2O3. The acetonide ring adopts an envelope conformation with one of the O atoms as the flap and the piperidine ring adopts a slightly twisted boat conformation. The absolute configuration was determined by use of d-ribose as the starting material. The compound exists as O-H⋯O hydrogen-bonded chains of mol-ecules running parallel to the b axis.

Glycosidase inhibition by all 10 stereoisomeric 2,5-dideoxy-2,5-iminohexitols prepared from the enantiomers of glucuronolactone.

The enantiomers of glucuronolactone are excellent chirons for the synthesis of the 10 stereoisomeric 2,5-dideoxy-2,5-iminohexitols by formation of the pyrrolidine ring by nitrogen substitution at C2 and C5, with either retention or inversion of configuration; the stereochemistry at C3 may be adjusted during the synthesis to give seven stereoisomers from each enantiomer. A definitive side-by-side comparison of the glycosidase inhibition of a panel of 13 glycosidases showed that 8 of the 10 stereoisomers showed significant inhibition of at least one glycosidase.

2-N-Benzyl-2,6-dide-oxy-2,6-imino-3,4-O-isopropyl-idene-3-C-methyl-d-allono-nitrile.

X-ray crystallography firmly established the relative stereochemistry of the title compound, C(17)H(22)N(2)O(3). The absolute configuration was determined by use of 2-C-methyl-d-ribonolactone as the starting material. The compound exists as O-H⋯N hydrogen-bonded chains of mol-ecules running parallel to the a-axis.

N-(2-Carb-oxy-eth-yl)-2,5-dide-oxy-2,5-imino-d-mannonic acid [(3R,4R,5R)-1-(2-carb-oxy-eth-yl)-3,4-dihy-droxy-5-hy-droxy-methyl-l-proline].

The absolute stereochemistry of the title compound, C(9)H(15)NO(7), was determined from the use of d-glucuronolactone as the starting material. The compound crystallizes as the zwitterion. The five-membered ring adopts an envelope conformation with the -CH(2)OH-substituted C atom forming the flap. An intramolecular N-H⋯O hydrogen-bond occurs. In the crystal, the compound exists as a three-dimensional O-H⋯O intermolecular hydrogen-bonded network with each mol-ecule acting as a donor and acceptor for four hydrogen bonds.

N-Benzyl-3,5-dide-oxy-3,5-imino-1,2-O-isopropyl-idene-ß-l-lyxofuran-ose.

X-ray crystallography confirmed the formation, structure and relative stereochemistry of the title compound, C(15)H(19)NO(3), which contains a sterically congested four-membered azetidine ring system. The absolute configuration was determined by the use of l-arabinose as the starting material.

4-C-Me-DAB and 4-C-Me-LAB - enantiomeric alkyl-branched pyrrolidine iminosugars - are specific and potent α-glucosidase inhibitors; acetone as the sole protecting group.

The syntheses of 4-C-Me-DAB [1,4-dideoxy-1,4-imino-4-C-methyl-d-arabinitol] from l-erythronolactone and of 4-C-Me-LAB [from d-erythronolactone] require only a single acetonide protecting group. The effect of pH on the NMR spectra of 4-C-Me-DAB [pK(a) of the salt around 8.4] is discussed and illustrates the need for care in analysis of both coupling constants and chemical shift. 4-C-Me-DAB (for rat intestinal sucrase K(i) 0.89 µM, IC(50) 0.41 µM) is a competitive - whereas 4-C-Me-LAB (for rat intestinal sucrase K(i) 0.95 µM, IC(50) 0.66 µM) is a non-competitive - specific and potent α-glucosidase inhibitor. A rationale for the α-glucosidase inhibition by DAB, LAB, 4-C-Me-DAB, 4-C-Me-LAB, and isoDAB - but not isoLAB - is provided. Both are inhibitors of endoplasmic reticulum (ER) resident α-glucosidase I and II.

Oxetanes from the ring contraction of alpha-triflates of gamma-lactones: oxetane nucleosides and oxetane amino acids.

Alpha-Triflates of gamma-lactones with potassium carbonate in methanol give efficient contraction of the ring to oxetane-1-carboxylates in which the oxygen substituent at C(3) of the oxetane is predominantly trans to the carboxylate at C(2), regardless of the stereochemistry of the starting triflate. The limitations of the procedure are discussed and compared with analogous reactions for the preparation of THF carboxylates. The potential of the contraction in the preparation of oxetane nucleosides (such as oxetanocin) and oxetane sugar amino acids (analogues of oxetin) as peptidomimetics with predisposition to form secondary structural motifs is illustrated.

N-Benzyl-1,3-dide-oxy-1,3-imino-l-xylitol.

The structure determination confirms the stereochemistry of the title compound, C(12)H(17)NO(3), which contains a four-membered azetidine ring system. The absolute configuration was determined by the use of d-glucose as the starting material. In the crystal, O-H⋯O and O-H⋯N hydrogen bonds link the mol-ecules into layers in the ab plane.

6-De-oxy-3,4-O-isopropyl-idene-2-C-methyl-l-galactono-1,5-lactone.

X-ray crystallography unequivocally confirmed the stereochemistry of the 2-C-methyl group in the title mol-ecule, C(10)H(16)O(5), in which the 1,5-lactone ring exists in a boat conformation. The absolute stereochemistry was determined by the use of d-ribose in the synthesis. The crystal exists as O-H⋯O hydrogen bonded chains of mol-ecules running parallel to the a axis with each mol-ecule acting as a donor and acceptor for one hydrogen bond.

2-Azido-2-de-oxy-3,4-O-isopropyl-idene-2-C-methyl-d-talono-1,5-lactone.

The relative stereochemistry of the title compound, C(10)H(15)N(3)O(5), was confirmed by the crystal structure determin-ation. The absolute configuration was determined from the use of d-lyxonolactone as the starting material. The six-membered ring adopts a boat conformation with the larger azide group, rather than the methyl group, in the bowsprit position. In the crystal structure, a bifurcated inter-molecular O-H⋯O/O-H⋯N hydrogen bond links mol-ecules into chains running parallel to the b axis.