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The stereochemical course of the osmium-mediated bis-hydroxylation of the allylic derivative 6c, whose the structure is closely related to that of a C-1/C-7 fragment of the title aglycone, has been established unambiguously by X-ray analysis of a carboxylic acid derived from one of the two diastereomeric diols which formed.

Thermal intramolecular Diels-Alder cyclisation of the ketone C-1 proceeds through an exo transition state to give the ketone CAT-2.

Oxidation of a THF solution of Li[HC(PPh 2 ) 2 ] with iodine affords the isomeric products Ph 2 P-CH=PPh 2 -PPh 2 =CH-PPh 2 2, (Ph 2 P) 2 C=PPh 2 -CH 2 -PPh 2 4 and (Ph 2 P) 2 CH-CH(PPh 2 ) 2 1, which result from P-P, P-C and C-C coupling, respectively. The latter pathway has now been established for the first time and the crystal structure of the resulting new chiral tetraphosphine 1 has been determined by X-ray diffraction.

The acetolysis with anhydrous acetic acid of the diazoketone 1 , prepared from potassium 1,2:3,4-di- O -isopropylidene-α- D -galacturonate, gave ketoacetates having the D - glycero ( 3 )and L - glycero ( 5 )configuration at C-7, together with the 3-oxetanone 7 , a product of pyranose-ring opening. Starting from the ketoacetates 3 and 5 , the lincosamine derivative, 6-acetamido-6,8-dideoxy-1,2:,4-di- O -isopropylidene -α- D - erythro - D - galacto -octopyranose ( 8 ), and its three diastereoisomers at C-6 and C-7 ( 9 , 10 , and 11 ) were obtained by oximation, reduction, and N -acetylation.

Stereospecific, Grignard addition reactions are described that afford C -phenyl branched-chain pentitols having either the D - arabino (2) or D - ribo (19) stereochemistry, according to the mode of substitution of the starting 2-pentulose. The reaction of 3,5- O -benzylidene-1-deoxy- D - erythro -2-pentulose (1) with phenyl-magnesium bromide led stereospecifically to 3,5- O -benzylidene-1-deoxy-2- C -phenyl- D -arabinitol (2) , the configuration of which was established by a nuclear Overhauser experiment with its 2,4:3,5-dibenzylidene acetal (3) . Acid hydrolysis of 2 led to the novel, crystalline 1-deoxy-2- C -phenyl- D -arabinitol (4) , further characterized as its triacetate 5 . In attempts to mask certain hydroxyl groups of 2 selectively, the 2,4- O -isopropylidene (6) and 2,4- O -carbonyl (7) derivatives, the 4-acetate 8 , the 4-(trimethylsilyl) and 4-( tert -butyldimethylsilyl) ethers ( 10 and 17 ), and the corresponding 2-phenylcarbamates 9 (from 8 ) and 11 (from 10 ) were prepared. Catalytic hydrogenolysis of the carbamates 9 and 11 resulted in deoxygenation of the benzylic center with inversion of configuration to give 2( S )-3,5- O -benzylidene-1,2-dideoxy-2- C -phenyl- D - erythro -pentitol ( 12 ; from 11 ) and its 4- O -acetyl analog 13 (from 9 ). Benzylation of the trimethylsilyl ether 10 afforded 2- O -benzyl-3,5- O -benzylidene-1-deoxy-2- C -phenyl-4- O -(trimethylsilyl)- D -arabinitol (15) , together with the corresponding 2,4-dibenzyl ether 14 . Acid hydrolysis of 15 yielded the crystalline, branched-chain, benzyl ether 16 . The tert -butyldimethylsilyl ether of 1 reacted with phenylmagnesium bromide to give, exclusively, the C -phenyl branched-chain pentitol (19) having the D - ribo stereochemistry.

Non-growing, washed cells of Escherichia coli, depressed for the synthesis of thiamine, were incubated in the presence of [1,1,1,5-2H4]-1-deoxy-D-threo-2-pentulose (9) in a medium containing the pyrimidine moiety of thiamine, L-tyrosine, and glucose. The thiamine thus biosynthesized was extracted and cleaved to give 5-(2-hydroxyethyl)-4-methylthiazole (HET) which was examined as the trifluoroacetate derivative by electron-impact mass spectrometry. The distribution of the label in the fragments indicated that the pentulose (9) was a precursor of the C5-chain of HET without C–C bond cleavage. Several routes to 1-deoxypentuloses are described. Condensation of 2,4-O-benzylidene-D-[4-2H1]threose (23) with trideuteriomethylmagnesium iodide gave the protected 1-deoxypentitols (24) and (25). Brominolysis of the mixed dibutylstannylidenes then afforded [1,1,1,5-2H4]-3,5-O-benzylidene-1-deoxy-D-threo-2-pentulose (26), which was converted into the free sugar (9) by acidic hydrolysis. 1-Deoxy-D-erythro-2-pentulose was prepared in similar manner. Condensation of 2-([2H3]-methyl)-1,3-dithian with 2,3-O-isopropylidene-D-glyceraldehyde, followed by a C-3 epimerization step also led, after deprotection, to a mixture of [1,1,1-2H3]-1-deoxy-D-erythro- and [1,1,1-2H3]-1-deoxy-D-threo-2-pentulose, (5) and (6).

Treatment of 1,2:3,4-di- O -isopropylidene-α- D -galactopyranuronyl chloride with diazoethane gave a diazoketone that was converted with methanol in the presence of boron trifluoride into a mixture of keto-ethers. One of these keto-ethers was transformed by reduction of its oxime and N -acetylation into a blocked derivative of celestosamine, which was found to be identical with 5 prepared from a natural source, i.e. lincomycine. The properties of the other two keto-ethers are in agreement with a ( D or L )- glycero - L - altro configuration ( 14 ) for one of them, and with the presence of a 3-oxetanone ring in the structure ( 18 ) of the other one.

The tripod ligand HC(PPh2)3 reacts with Mo(CO)3(CH3CN)3 yielding Mo(CO)3(CH3CN)(HC(PPh2)3). Reaction of this Mo0 complex with [Rh(CO)2Cl]2 gives unexpectedly the tetranuclear species [Rh2(CO)(HC(PPh2)3)]2(μ-Cl)+3 (3) which crystallizes as the Rh(CO)2Cl−2 salt (3a). This complex crystallizes in the monoclinic space group P21/c with Z = 4, with all dimensions a = 19.685(3), b = 19.524(3), c = 22.657(4) A, and β = 96.96(2)°. A direct route to the PF−6 salt of 3 (3b) is also presented. The 31P NMR data show 3a and 3b to be identical and that the tetranuclear structure is retained in solution, i.e. two units of binuclear RhI species bridged by three chlorine atoms. In each binuclear unit, the tripod ligand spans two RhI which are linked directly by a metal-metal bond (RhRh = 2.696 A).

Non growing washed cells of Escherichia coli, derepressed for the biosynthesis of thiamine, have been incubated in the presence of glucose and either 1-deoxy- D -threo-2-pentulose 1 or 1-deoxy- D -erythro-2-pentulose 2 trideuterated on the methyl group. The incorporation of deuterium into the thiazole moiety of thiamine was measured by mass spectrometry. The label of the threo-compound was found in more than 40% of the thiazole biosynthesized in its presence; the label of the erythro-compound in less than 5%. Hence it is likely that the carbon chain of 1-deoxy- D -threo-2-pentulose is the precursor of the five carbons chain of the thiazole moiety of the thiamine molecule in E. coli.

Le premier compose du titre cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /c. Le second cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /n. Affinement de la structure jusqu'a 3,5% et 2,9% respectivement

Gegenuber dem fruheren Verfahren konnte die Pentulose (II) in wesentlich besserer Ausb. aus der Ulose (I) mittels LiOH in einem Zweiphasen-System erhalten werden.

The crystal and molecular structure of (1S)-5,7-anhydro-8-deoxy-1,2 :3,4-di-O-isopropylidene-1-O-methyl-D-glycero-D-galacto-octos-6-ulose has been determined by X-ray analysis. It crystallizes in the tetragonal P41(P43) space group, with a=b= 10.239(5), c= 16.369(7)A, Z= 4. The structure was solved by direct methods and refined to an R value of 5.3%. The octose chain is bent in such a way as to keep C-2, -3, -4, and -5 in the same plane. The formation of this compound during the methanolysis of 7,8-dideoxy-7-diazo-1,2 :3,4-di-O-isopropylidene-α-D-galacto-octos-6-ulopyranose(3) by participation of the pyranose ring oxygen atom is discussed in the light of current ideas on diazo-ketone substitution.