Acid-catalyzed isomerization and dehydration of dl-glyceraldehyde and 1,3-dihydroxy-2-propanone

The interconversion of 2,3-dihydroxypropanal (1) and 1,3-dihydroxy-2-propanone (3) and their dehydration to pyruvaldehyde (5) has been studied in 0.5m sulfuric acid at 100°. The conversion of 1 and 3 into 5 under these conditions, in tritiated water, was monitored by isolation of 5 and determination of the distribution of carbon-bound tritium (namely, that at the aldehyde and methyl groups). This was accomplished by conversion of 5 into the phenylosazone and counting, and by conversion of 5 into pyruvic acid (isolated as the p-nitrophenylhydrazone), counting, and a difference calculation. In all cases negligible activity (about 0.8 % the activity of the solvent) was found at the aldehyde carbon of 5, derived from either 1 or 3, and parallel chromatographic studies indicated only a small extent of interconversion. As 5 incorporated tritium under conditions of its formation, plots of incorporation versus time were made and the curves extrapolated to zero time, in order to determine initial activity at the methyl group of 5, derived from either 1 or 3. This method showed that the 5 derived from 3 contained 10 % of the activity of the solvent at the methyl group as it was produced, whereas the 1-derived 5 contained no activity. In another experiment, [2-³H]1 was prepared and converted into 5. The resulting 5 was found to be labeled at C-3, indicating at C-2 → C-3 intramolecular, hydrogentransfer reaction during the conversion of 1 into 5.     

2-Carboxy-4-hydroxy-α-tetralone,a precursor for catalponol biosynthesis

2-Carboxy-4-hydroxy-α-tetralone (5) and its methyl ester (10) were incorporated into catalponol (1) in Catalpa ovata with retention of C-4 and C-8 tritium atoms. Incorporation of the former two substances into catalpalactone (2) and 4,9-dihydroxy-α-lapachone (12) was also demonstrated.     

Electrolytic reduction of abscisic acid methyl ester and its free acid

Abscisic acid (ABA, 1), a plant hormone, has electrophilicity derived almost entirely from the side-chain, 3-methylpenta-2,4-dienoic acid. The electrochemical property of ABA was investigated by analysis of its cathodic reaction. ABA methyl ester (1-Me) was reduced at a peak potential of −1.6 V to give a unique and unstable bicyclic compound (5-Me) as a major product at pH 3 and 7. This finding showed that an electron was absorbed in the conjugated dienecarboxyl group, and that C-5 with a high electron density attacked C-2′ through an intramolecular nucleophilic addition. At pH 10, in addition to 5-Me, a compound 4-Me was formed by isomerization of 5-Me under alkaline conditions. For a cathodic reaction of ABA at pH 3 and 7, compound 5 was a major product as well as in the case of ABA methyl ester. However, at pH 10, a dimer (6) with an epoxy group, 1′-deoxy-ABA (7) and other compounds were formed instead of compounds 4 and 5. Compounds 4 and 5 were biologically inactive, suggesting the importance of the electrophilic side-chain of ABA for biological activity.     

Novel nucleosides as potent influenza viral inhibitors

Influenza virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified ((2R,3S,4R,5R)-3-acetoxy-5-(4-benzamido-2-oxopyrimidin-1(2H)-yl)-4-fluoro-3,4-dimethyl-tetrahydrofuran-2-yl) methyl benzoate (18c) as a potent influenza virus inhibitor. We now here report the synthesis and evaluation of a series of C-3′ modified ribose nucleosides. These novel compounds were prepared, primarily by taking known ((2R,3R,4R)-3-benzoyloxy-4-fluoro-4-methyl-5-oxo-tetrahydrofuran-2-yl)methyl benzoate (1) and converting it in to C-3 keto sugar (7), reacting C-3 keto group with methyl magnesium bromide, followed by coupling these sugars with purine and pyrimidine bases. Anti influenza viral activity was determined by screening against both A and B viral strains.     

Stereochemistry of the β-cyanoalanine synthetase and S-alkylcysteine lyase reactions

The stereochemistry of the replacement of the SH-group of cysteine by CN catalyzed by β-cyanoalanine synthetase was studied using cysteine stereospecifically tritiated at C-3. Analysis of the resulting β-cyanoalanine by conversion into fumarate via aspartate and malate showed that the reaction had occurred with retention of configuration at C-3. Using cystine stereospecifically labeled at C-3 with tritium or with tritium and deuterium, it was found that the α,β-elimination reaction catalyzed by S-alkylcysteine lyase involves stereo-specific replacement of the β-substituent of the substrate by a hydrogen derived from the solvent, D₂O or H₂O, with retention of configuration to give pyruvate containing a chiral methyl group. The results are discussed, particularly in the light of mechanistic proposals by Braunstem and co-workers.     

The acid-catalyzed dehydration of 1-benzylamino-1-deoxy-d-threo-pentulose, 1-dibenzylamino-1-deoxy-d-fructuronic acid,and d-glucuronic acid

Three compounds, 1-benzylamino-1-deoxy-d-threo-pentulose (1), 1-dibenzylamino-1-deoxy-d-fructuronic acid (2), and d-glucuronic acid (3) were converted into 2-furaldehyde in acidified, tritiated water. In the latter system, the 2-furaldehyde derived from 1 contained 13% of the activity of the solvent at the aldehyde carbon and 9% at positions 3–5 of the furan ring; that from 2 contained 8% at the aldehyde carbon and 29% at positions 3–5; and that from 3 contained 18% at positions 3–5 In deuterium oxide, the 2-furaldehyde derived from 1 contained 14 atom % of deuterium at position 3, 5% at position 4, and 0% at position 5. That from 2 contained 50% at position 3, 44% at position 4, and 7% at position 5. That from 3 contained 35% at position 3, 15% at position 4, and 5% at position 5. The data for 1 are discussed relative to prior data on incorporation collected for d-xylose Incorporation data for both 2 and 3 are qualitatively consistent with a decarboxylation step involving a β,γ-unsaturated, carboxylic acid intermediate. A mechanism for the decarboxylation of hexuronic acids is presented.     

Trichodiene biosynthesis and the stereochemistry of the enzymatic cyclization of farnesyl pyrophosphate

Cyclization of trans,trans-[1-³H₂,12,13-¹⁴C]farnesyl pyrophosphate (2a) by a preparation of trichodiene synthetase isolated from the fungus, Trichothecium roseum, gave trichodiene (5a), which was shown by chemical degradation to retain both tritium atoms of the precursor at C-11. Incubation of 1S-[1-³H,12,13-¹⁴C]farnesyl pyrophosphate (2b) and 1R-[1-³H,12,13-¹⁴C]farnesyl pyrophosphate (2c) with trichodiene synthetase and degradation of the resulting labeled trichodienes, 5b and 5c, established that the displacement of the pyrophosphate moiety from C-1 of the precursor and formation of the new C-C bond in the formation of trichodiene takes place with net retention of configuration. These results are accounted for by an isomerization-cyclization mechanism involving the intermediacy of nerolidyl pyrophosphate (4).     

An intramolecular C-2 → C-1 hydrogen transfer during the acid-catalyzed conversion of d-xylose to d-threo-pentulose (d-xylulose)

Aldose-ketose isomerases are known to catalyze a partial and sometimes complete intramolecular hydrogen transfer between C-1 of the ketose and C-2 of the aldose. It was recently shown (Feather, M. S., and Harris, D. W. (1975) J. Amer. Chem. Soc.97, 178–181) that the same type of transfer occurs during the acid-catalyzed interconversion of d-fructose, d-glucose, and d-mannose. A similar transfer is demonstrated herein for the conversion of d-xylose to d-xylulose in acid solution. d-[2-³H]xylose was isomerized in aqueous sulfuric acid and the resulting d-[³H]xylulose was isolated in 6% yield. The ketose had 18.3% the activity of the starting aldose. Chemical degradation showed that all the carbon-bound tritium of the d-[³H]xylulose was located at C-1, thus indicating a C-2 → C-1 intramolecular hydrogen transfer. During the reaction, less than 1.2% of the total radiochemical activity was found in the solvent, and, the unreacted d-[2-³H]xylose was recovered, having an activity nearly the same as the starting material. The differences in activity, therefore, of the d-[2-³H]xylose and the d-[1-³H]xylulose are due to an isotope effect ($\text{K}{}_{\mathrm{<mtext>H</mtext>}}\text{K}{}_{\mathrm{<mtext>T</mtext>}}$) which is indicated to be 5.4. The data are discussed in terms of currently accepted models for isomerase mechanisms.     

Preparation and characterization of novel 4-bromo-3,4-dimethyl-1-phenyl-2-phospholene 1-oxide and the analogous phosphorus heterocycles or phospha sugars

4-Bromo-3,4-dimethyl-1-phenyl-2-phospholene 1-oxide (3c) was first synthesized from 3,4-dimethyl-1-phenyl-2-phospholene 1-oxide (2c) by a bromo-radical substitution reaction occurred at C-4 position by N-bromosuccinimide and 2,2′-azobisisobutyronitrile. The novel phospha sugar analogue 3c exerted high anti-proliferative effect on U937 cells evaluated by MTT in vitro methods and was much more efficient than that of Gleevec®, which is known as a molecule targeting chemotherapeutical agent. The substitution of 2-phospholenes at C-3 and C-4 position with methyl groups as well as 4-bromo substituent suggests a good anti-proliferative effect.     

Reaction of acylated methyl arabinosides with hydrogen bromide

Treatment of methyl tri-O-acetyl-β-D-arabinopyranoside (1a) with hydrogen bromide in benzene or in acetic acid gave, in addition to the pyranosyl bromide (2a), a considerable proportion of tri-O-acetyl-D-arabinofuranosyl bromide (5). Similar treatment of methyl tri-O-benzoyl-β-D-arabinopyranoside (1b) gave a good yield of the pyranosyl bromide (2b); no furanoid derivative was formed. Ring contraction also took place when methyl 4-O-acetyl-2,3-di-O-benzoyl-β-D-arabinopyranoside (7) was treated with hydrogen bromide, whereas the isomeric 3-O-acetyl-2,4-di-O-benzoyl compound (12) gave the pyranosyl bromide 13 in high yield. Thus, methyl pyranosides with an O-acetyl group at C-4 undergo ring contraction on treatment with hydrogen bromide. The corresponding compounds with O-benzoyl groups at C-4 gave pyranosyl bromides only.     

Alstiphyllanines E–H,picraline and ajmaline-type alkaloids from Alstonia macrophylla inhibiting sodium glucose cotransporter

Three new picraline-type alkaloids, alstiphyllanines E–G (1–3) and a new ajmaline-type alkaloid, alstiphyllanine H (4) were isolated from the leaves of Alstonia macrophylla together with 16 related alkaloids (5–20). Structures and stereochemistry of 1–4 were fully elucidated and characterized by 2D NMR analysis. Alstiphyllanines E and F (1 and 2) showed moderate Na⁺-glucose cotransporter (SGLT1 and SGLT2) inhibitory activity. A series of a hydroxy substituted derivatives 21–28 at C-17 of the picraline-type alkaloids have been derived as having potent SGLT inhibitory activity. 10-Methoxy-N(1)-methylburnamine-17-O-veratrate (6) exhibited potent inhibitory activity, suggesting that the presence of an ester side chain at C-17 may be important to show SGLT inhibitory activity. Structure activity relationship of alstiphyllanines on inhibitory activity of SGLT was discussed.     

Loranthin: A new polyhydroxylated flavanocoumarin from Plicosepalus acacia with significant free radical scavenging and antimicrobial activity

A new flavanocoumarin, loranthin (1) together with catechin (2), quercetin (3) rutin (4), gallic acid (5) and methyl gallate (6) were isolated from Plicosepalus acacia. Loranthin possesses the rare flavanocoumarin skeleton in which the flavan and coumarin moieties are linked via C-7/C-8 of both moieties. The flavan moiety in 1 was found to be catechin, while a 3,5,6,7-tetrahydroxycoumarin fragment represented the other moiety in 1. The structures of the isolated compounds were established based on different spectroscopic data including HRFABMS, 1D and 2D NMR (COSY, HSQC, and HMBC). The free radical scavenging activities of different extracts and pure compounds were determined using DPPH reagent and all the tested samples revealed significant activities with variable percent. Loranthin exhibited a 38.4% inhibition in the free radical scavenging assay. The antimicrobial activity of loranthin was evaluated against several pathogen and loranthin displayed significant effect against Staphylococcus aureus. Moreover, the inhibition activity of the compounds against several disease-relevant protein kinases were also evaluated and discussed.     

Decomposition reactions of amino sugars: the dehydration of 2-amino-2-deoxy-D-glucose

The stability of the title compound (1) was investigated at 100° in acidified aqueous solutions containing, in some instances, glycine or pyridine. In strong acid (3M hydrochloric acid), the sugar was relatively stable, and no identifiable decomposition-products were observed. In less-acidic solutions (≤0.5M hydrochloric acid) in the presence of glycine, substantial decomposition occurred with the production of 5-(hydroxymethyl)-2-furaldehyde (2) in 0.5-5.2% yield. The major dehydration products, however (up to 18% of the starting sugar), were pyrazine derivatives bearing dissimilar, four-carbon, acyclic-sugar side-chains attached to C-2 and C-5 of the ring, respectively, arising, most probably, from C-3-C-6 of the original sugar molecules. When the conversions were performed in deuterium oxide solution, carbon-bound isotope was observed in 2 (at the aldehyde carbon and at C-3) and, in the pyrazine derivatives, on the ring (positions 3 and 6), and on the sugar-derived, side-chains.     

The synthesis of 3-amino-2,3,6-trideoxy-l-xylo-hexopyranose derivatives

Derivatives (the 3-acetamido-4-benzoate 12, the 3-acetamido-4-acetate 13, and the N-acetyl derivative 14) of the methyl glycoside of the title sugar were prepared in a sequence of high-yielding steps from methyl 3-azido-4,6-O-benzylidene-2,3-di-deoxy-α-d-arabino-hexopyranoside (4). N-Bromosuccinimide converted 4 into the crystalline 4-O-benzoyl-6-bromide 5, which was treated with silver fluoride to afford the 5,6-unsaturated glycoside 6. Catalytic hydrogenation of 6 led, essentially, to a 7:1 mixture of 12 and its 5-epimeric d-arabino isomer 7. Alternatively, 6 was debenzoylated to 10, and the latter treated with lithium aluminum hydride to give crystalline methyl 3-amino-2,3,6-trideoxy-α-d-threo-hex-5-enopyranoside (11). Reduction of 11 (as its salt) by hydrogen, with subsequent N-acetylation, furnished the methyl β-l-xylo-glycoside 13 almost exclusively, with net inversion at C-5. Compound 13 was readily converted into the crystalline target compound 14. When dehydrobromination by silver fluoride was attempted with the 3-acetamido analog (2) of 5, a 3,6-anhydro product (1) was obtained, instead of the expected 5,6-alkene 3.     

Conversion of allyl 2-acetamido-2-deoxy-β-d-glucopyranoside into 2-methyl-(3,4,6-tri-O-benzoyl-1,2-dideoxy-α-d- galactopyrano)-[2′,1′:4,5]-2-oxazoline

2-Methyl-(3,4,6-tri-O-benzoyl-1,2-dideoxy-α-d-galactopyrano)-[2′,1′:4,5]-2-oxazoline (7) was prepared from 1-propenyl 2-acetamido-3,4,6-tri-O-benzoyl-2- deoxy-β-d-galactopyranoside (6). The latter was prepared from allyl 2-acetamido-2-deoxy-β-d-glucopyranoside (1) through selective benzoylation at O-3 and O-6, conversion into the 4-p-bromobenzenesulfonate 4, inversion of configuration at C-4 to afford allyl 2-acetamido-3,4,6-tri-O-benzoyl-β-d-galactopyranoside (5), and subsequent isomerization with palladium-charcoal to give 6.     

Microbial transformations of flavanone by Aspergillus niger and Penicillium chermesinum cultures

As a result of biotransformation of flavanone (1) by the strain Aspergillus niger MB (being the UV mutant) and by the wild strain Penicillium chermesinum 113 the products of hydroxylation at C-6 (2) and C-4′ (5) were obtained. Additionally, three dihydrochalcones with hydroxyl groups at C-2′ (4), C-2′ and C-5′ (3) and C-2′ and C-4 (6) were formed.     

Changes in the hemicellulosic polysaccharides of rye-grass with increasing maturity

Reaction of the C-2 mercurated methyl hexopyranoside acetates 1–3 with an excess of iodine resulted in nearly quantitative replacement of mercury by iodine with retention and inversion of configuration at C-2. Similar replacement was observed with 2-acetoxymercuri-3,4,6-tri-O-acetyl-2-deoxy-α-d-glucopyranose (4). In the iodinolysis of 2-acetoxymercuri-1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-glucopyranose (5) in methanol, however, replacement at C-2 was accompanied to a considerable extent by solvolysis of the 1-acetoxyl group, and a mixture of 1,2-trans isomers of methyl 3,4,6-tri-O-acetyl-2-deoxy-2-iodo-hexopyranosides having the d-gluco and d-manno configurations was obtained, together with 1,3,4,6-tetra-O-acetyl-2-deoxy-2-iodo-α-d-mannopyranose.     

The synthesis of [3H]gibberellin A3 and [3H]gibberellin A1 by the palladium-catalyzed actions of carrier-free tritium on gibberellin A3

Reaction of gibberellin A₃ (GA₃) with carrier-free tritium gas and 5% palladium on calcium carbonate as catalyst gave a complex mixture of products, several of which were isolated and identified. Three of the purified products are the radioactive forms of naturally occurring gibberellins: [³H]GA₃ (1), [³H]GA₁ (2) and [³H]tetrahydro GA₃ (4). Another substance was isolated and tentatively identified as [³H]16,17-dihydro GA₃ (3). GLC was used to determine the specific activities of 1 and 2. [³H]GA₃ likely arises from palladium catalysed nonspecific exchange of GA₃ alkane hydrogen atoms with tritium. [³H]GA₁ is also exchange labeled but most of its radioactivity is due to tritium addition to the C-1,2 olefinic bond of GA₃.     

Resolution of anomeric 2-amino-2-deoxy-d-glycofuranosides and -glycopyranosides by cation-exchange chromatography

Methyl 4,6-O-benzylidene-2-deoxy-α-D-ribo-hexopyranoside (1) is converted into methyl 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-α-D-ribo-hexopyranoside (3) via the 3-O-benzoyl derivative (2) of 1 by subsequent treatment with N-bromosuccinimide. Compound 3 is the key intermediate in high-yielding, preparative syntheses of the title dideoxy sugars, which are constituents of many antibiotics. Dehydrohalogenation of 3 affords the 5,6-unsaturated glycoside 7. which undergoes stereospecific reduction by hydrogen with net inversion at C-5 to give methyl 3,4-di-O-benzoyl-2,6-dideoxy-β-L-lyxo-hexopyranoside (8), whereas reductive dehalogenation of 3 provides the corresponding D-ribo derivative 4. The unprotected glycosides 9 (L-lyxo) and 5 (D-ribo) are readily obtained by catalytic transesterification, and mild, acid hydrolysis gives the crystalline title sugars 10 (L-lyxo) and 6 (D-ribo) in 45 and 57% overall yield from 1 without the necessity of chromatographic purification at any of the steps.     

Chemistry and biology of trehazolins

Trehazolin (1) is a unique natural pseudodisaccharide possessing strong trehalase-specific inhibitory activity. To determine its argued correct stereochemistry, the syntheses of trehazolin (1), its components, the aglycon moiety, trehalamine (4) and its aminocyclitol hexaacetate (6), were accomplished from d-glucose using intramolecular [3+2] cycloaddition as the key step. In order to investigate the structure–activity relationships with regard to the stereochemistry of the aminocyclitol moiety and that of the anomeric position of trehazolin (1), trehalostatin (2) (trehazolin C-5 epimer), trehazolin β-anomer (32) and, trehazolin C-6 epimer (33) were all synthesized. In particular, with respect to the synthesis of trehazolin C-6 epimer (33), a tandem aldol–Wittig type reaction was developed as the key step to synthesize the highly functionalized 5-membered cyclitol. Moreover, on the basis of the outcome of these synthetic studies, a number of trehazolin-related compounds (49–52), modified at the terminal amino group of trehalamine (4), were synthesized to be evaluated as candidates directed to anti-NIDDM (non-insulin-dependent diabetes mellitus) drugs.