Mannopyranoside

Because of this situation, the prospect of synthesizing D-rhamnosyl cardenolides containing the unnatural, a-D-linkage was investigated. D-Rhamnose has not been reported to occur naturally, but it has been synthesized by Hudson and co-workers (4) in six steps, starting with methyl a-D-mannopyranoside. An intermediate in the synthesis is methyl... 

Methyl a-D-mannopyranoside was treated in succession with p-toluene-sulfonyl chloride, carbonyl chloride, and benzoyl chloride, and, without isolating the intermediates, there was obtained in 37% yield methyl 4-0-l enzoyl-2,3-O-carbony 1-6-0-(p-tolylsulfonyl ) -D-mannoside. The tos-yloxyl group of the latter was replaced by iodine, and hydrogenation of the 6-iodo derivative in the presence of a nickel boride catalyst gave methyl 4-0-benzoyl-2,3-0-carbonyl-6-deoxy- -D-mannoside. Treatment of the latter with hydrogen bromide in acetic acid gave crystalline 4-0-benzoyl-2,3-0-carbonyl-6-deoxy-a-D-mannosyl bromide (8) (16). The... 

A mixture of d- and l- hexoses also results from the hydroboration of these 5-enes. Hydroboration results in anti-Markownikoff, cw-hydration of the double bond and the amount of each hexose formed varies according to the nature of the substituent groups. For example, hydroboration (23) of methyl 6-deoxy-a-D-ryZo-hex-5-enopyranose (3) affords methyl a-D-glucopyranoside and methyl / -L-idopyranoside in the ratio of 1 2.5 respectively whereas hydroboration of the fris-trimethylsilyl ether of 3 afforded them in the ratio 1 0.6 respectively. The hydroboration method can be used to achieve specific labelling of hexoses with tritium methyl-/ -L-idopyranoside[5-H3] and methyl a-D-glucopyranoside [5-H3] were thus prepared (23). Similarly, hydroboration of the D-Zt/ro-hex-5-eno derivative (14) with diborane-H3 followed by removal of the isopropyli-dene group, afforded methyl a-D-mannopyranoside [5-H3] and methyl / -L-gulopyranoside [5-H3] in the ratio of 1 2 respectively (23). 

This section is completed with a brief review of the synthesis and properties of this epimer (20) of the precursor of thiazole in bacteria. This pentulose is conveniently accessible by an unconventional route (Scheme 19). Methyl 2,3 4,6-di-O-isopropylidene-a-D-mannopyranoside, readily available from methyl ot-D-mannopyranoside, is converted to the ketonic glycoside by butyllithium in 91% yield, following a method first published by Klemer and Rodemeyer43 and scaled up by Horton and Weckerle.44 This was converted by means of lithium hydroxide in a water-ether mixture into 3,5-0-benzylidene-l-deoxy-D-eryf/iro-2-pen-tulose in 55% yield. Hydrolysis to the free pentulose (20) proceeded in 73% yield in aqueous acetic acid. This product was obtained as a syrup with a characteristic absorption band at 1705 cm 1 as a film. Thus, there is a fair proportion of the open-chain ketone under these conditions, as with the D-threo epimer.45... 

Figure 4 The structure of pentameric methyl-4,6-0-benzylidene-2,3-0-dibutylstannylene-a-D-mannopyranoside. ...

CN, coordination number. A CN of 5-6 means that the compound contains the Sn central atom in two different environments. 1, Bu2Sn0CH2CH20 2, methyl-4,6-0-benzylidene-a-D-glucopyranoside 3, methyl-4,6-0-benzylidene-a-D-mannopyranoside 4, o-lactobionic acid 5, o-galactose 6, Bu2Sn-DNA, maleic acid. 

D-mannopyranoside [41]. All these anions were isolated as their dimethylam-monium salts in good yields and chemical purity. The presence of the stereo-genic centers of the chiral ligands induces the formation of diastereomers. In essentially all cases, the initial salts are obtained in high diastereomeric purity. Figure 20 shows the diastereomeric ratios and, when known, the relative configuration of the major isolated compounds. 

Similarly, the mannopyranosyl analog (346) was synthesized by condensation of di-O-isopropylidene-a-DL-carba-mannopyranose (349) with 348. The other isomer (347) was obtained by reaction of 278 with tetra-O-benzoyl-a-D-mannopyranosyl bromide (350). The four carba-glucopyrano-syl D-mannopyranosides, including 346 and 347, show no antiviral activity. 

As part of a study on cell-surface glycans, 2,3-bis(tetradecyloxy)propyl 2-deoxy-2-fluoro-a- and - -D-mannopyranosides were prepared by condensation of 3,4,6-tri-0-benzyl-2-deoxy-2-fluoro-a-D-mannopyranosyl chloride with 2,3-bis(tetradecyloxy)propanol. 

IC with bovine enzyme which is very similar to the human one. Inhibitor concentration for 50% inhibition. K of substrate (phenyl a-D-mannopyranoside). K of substrate (4-nitrophenyl a-D-manno-pyranoside). K of substrate (4-nitrophenyl D-glucosiduronic acid). K of substrate (4-nitrophenyl 2-acetamido-2-deoxy- o-glueoside). Inhibitors were chitotetraono-1,5-lactone and chitotetraose, respectively. 

To distinguish between these possibilities, Birch and Mylvaganam studied the effect of the sweetness of sucrose and the bitter-sweetness of methyl a-D-mannopyranoside on the bitterness of quinine sulfate, and the effect of the bitterness of quinine sulfate and methyl a-D-mannopyranoside on the sweetness of sucrose. A significantly diminished sweetness-response... 

Ci4HlfiOs Methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside MABMPY 30 454... 

CisH22Oi0 Methyl 2,3,4,6-tetra-O-acetyl-a-D-mannopyranoside MTAMAN 34 372... 

Ci8h23io9s Methyl 3,4-di-0-acetyl-6-deoxy-6-iodo-2-0-p-tolylsuIfonyl-a-D-mannopyranoside ADITSM 38 470... 

Methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-di(phenylazo)-a-D-mannopyranoside MBYZMN 38 479... 

The bicyclooctane sulfite illustrated can be oxidized with Ru04 to the sulfate in 72% yield.[29] The mannopyranoside sulfate was obtained by means of Af,N -sulfonyldiimi-dazole (ImSO2Im).[30] A trifold cyclic sulfate was synthesized according to route b.t31]... 

Thermal phosphitylation of methyl a-D-mannopyranoside (3) with P(NMe2)3 in pyridine or tetramethylurea gave 40% of a-methyl-D-mannopyranoside - 2,3,6-bicyclophosphite (4a). It underwent acetylation giving the corresponding acetate 4b sulfuration, and selenation afforded the corresponding pentavalent thio (4c) and seleno (4d) derivatives, respectively (Scheme 2). The trivalent acetate 4b was found to react with CuBr, Rh(CO)2(acac) and Cl2 [17]. 

Scheme 2 Phosphitylation of methyl (X-d-mannopyranoside (3) with P(NMe2)3...

Based on the fact that methyl 2,3-anhydro-a-D-mannopyranoside (II) is hydrolyzed17 by sodium methoxide to give, on subsequent methyla-tion, a mixture of two methyl trimethyl hexosides (methyl 3,4,6-trimethyl-a-D-altropyranoside and methyl 2,4,6-trimethyl-a-D-glucopyranoside) it was anticipated that the action of ammonia on II would follow essentially the same course. This was found to be the case, for with ammonia II yielded compounds which were converted to methyl 4,6-dimethyI-3-aeetamido-a-altropyranoside (III) and methyl 4,6-dimethyl-2-acetamido-a-D-glucopyranoside (IV) (10% yield). 

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