Synthesis of glycosides of 3-deoxy-4-thiopentopyranosid-2-uloses and their reduction products: 3-deoxy-4-thiopentopyranosides

Michael addition of common thiols to the enone system of (2S)-2-benzyloxy-2H-pyran-3(6H)-one (1) afforded the corresponding 3-deoxy-4-thiopentopyranosid-2-ulose derivatives (2-4). The reaction was highly diastereoselective, and the addition was governed by the quasiaxially disposed 2-benzyloxy substituent of the starting pyranone. As expected from the enantiomeric excess of 1 (ee > 86%) the corresponding thiouloses 2-4 exhibited the same optical purity. However, the enantiomerically pure thioulose 5 was obtained by reaction of 1 with the chiral thiol, N-(tert-butoxycarbonyl)-L-cysteine methyl ester. The thio derivative 7 was also synthesized by reaction of 6 (enantiomer of 1) with the same chiral thiol. Alternatively, 4-thiopent-2-uloses 9-12 were prepared in high optical purity by 1,4-addition of thiols to (2S)-[(S)-2'-octyloxy]dihydropyranone 8. Similarly, reaction of 13 (enantiomer of 8) with benzenemethanethiol afforded 14 (enantiomer of 10). This way, the stereocontrol exerted by the anomeric center on the starting dihydropyranone led to 4-thiopentuloses of the D and L series. Sodium borohydride reduction of the carbonyl function of uloses 10 and 12 gave the corresponding 3-deoxy-4-thiopentopyranosid-2-uloses (16-19). The diastereomers having the beta-D-threo configuration (16, 18) slightly predominated over the beta-D-erythro (17, 19) analogues. However, the reduction of the enantiomeric pyranones 10 and 14 with K-Selectride was highly diastereofacial selective in favor of the beta-D- and beta-L-threo isomers 16 and 20, respectively.     

Preparation of 3-deoxy-3-deuteroestrone and 3-deoxy-4-14C-estrone

3-Deoxy-3-deuteroestrone (1,3,5(10)-estratrien-17-one-3-d) and 3-deoxy-4-¹⁴C-estrone (1 ,3 ,5(10)-estratrien-17-one-¹⁴C) have been prepared. The mechanism of reductive dehalogenation of aryl iodides with lithium aluminum deuteride is discussed. The ¹³C-NMR spectrum of 3-deoxy-3-deuteroestrone is discussed.     

Preparation of 6-deoxy-6-fluorocellulose

6-Deoxy-6-fluorocellulose was prepared from cellulose 2,3-diacetate (1) or cellulose 2,3-dibenzoate (2) in various solvents, and was characterized by ¹⁹F and ¹³C NMR measurements. The best product, having ds of 0.95 at C-6 and 0.04 at C-3, was prepared from cellulose 2,3-dibenzoate in nitrobenzene. Other combinations of starting material and solvent gave a lower (≈ 0.8) ds of fluorine at C-6 and higher (≈ 0.12) at C-2 or C-3. Substitution at C-2 was observed when the combination of 1 and 1,4-dioxane, or 2 and chloroform was used. The products substituted at C-2 by fluorine were relatively resistant to acid hydrolysis.     

A new -2-haloacid dehalogenase acting on 2-haloacid amides: purification, characterization, and mechanism

-2-Haloacid dehalogenase catalyzes the hydrolytic dehalogenation of - and -2-haloalkanoic acids to produce the corresponding - and -2-hydroxyalkanoic acids, respectively. We have constructed an overproduction system for -2-haloacid dehalogenase from Pseudomonas putida PP3 ( -DEX 312) and purified the enzyme to analyze the reaction mechanism. When a single turnover reaction of -DEX 312 was carried out in H₂¹⁸O by use of a large excess of the enzyme with - or -2-chloropropionate as a substrate, the lactate produced was labeled with ¹⁸O. This indicates that the solvent water molecule directly attacked the substrate and that its oxygen atom was incorporated into the product. This reaction mechanism contrasts with that of -2-haloacid dehalogenase, which has an active-site carboxylate group that attacks the substrate to displace the halogen atom. -DEX 312 resembles -2-haloacid dehalogenase from Pseudomonas sp. 113 ( -DEX 113) in that the reaction proceeds with a direct attack of a water molecule on the substrate. However, -DEX 312 is markedly different from -DEX 113 in its substrate specificity. We found that -DEX 312 catalyzes the hydrolytic dehalogenation of 2-chloropropionamide and 2-bromopropionamide, which do not serve as substrates for -DEX 113. -DEX 312 is the first enzyme that catalyzes the dehalogenation of 2-haloacid amides.     

Total syntheses and cytotoxicity of kealiiquinone, 2-deoxy-2-aminokealiiquinone and analogs

Concise syntheses of two Leucetta-derived naphthimidazole alkaloids, kealiiquinone and 2-deoxy-2-aminokealiiquinone, are described based on a biosynthetic-guided hypothesis. Advanced intermediates containing the full naphthimidazole framework are constructed through Friedel–Crafts chemistry followed by oxidation of the electron rich C-ring with hydrogen peroxide. The cytotoxicity of these alkaloids in a breast cancer cell line along with several closely related marine-derived natural products kealiinines A–C and analogs are reported.     

Preparation of Methyl 4,6-O-benzylidene-2-deoxy-2-nitro-β-D-glucopyranoside from the corresponding 3-deoxy-3-nitro derivatives with sodium nitrite

Treatment of methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitro-β-D-erythro-hex-2-enopyranoside (2) with nitrous acid afforded the title 2-nitro sugar (4). The same product was also prepared by heterogeneous reaction of methyl 2-O-acetyl-4,6-O-benzylidene-3-deoxy-3-nitro-β-D-glucopyranoside (1) with sodium nitrite in the presence of a phase-transfer catalyst. Acid hydrolysis of 4 gave methyl 2-deoxy-2-nitro-β-D-glucopyranoside (7). Acetylation of 4, followed by elimination of acetic acid, afforded a 2-nitroalkene (6). 71e 3-acetate 5 reacted with ammonia, dimethylamine, and 2,4-pentanedione to give the products 8, 9, and 10, respectively, having the gluco configuration.