Acosamine

Several approaches based on nitro-aldol for the synthesis of amino sugars have been reported Alumina-catalyzed reaction of methyl 3- nitropropanoate with O-benzyl-o-lactaldehyde gives the o-ribo-nitro-aldol fanti, and isomeri in 63% yield, which is converted into L-dannosamine fsee Secdon 3 3 Jager and coworkers have reported a short synthesis of L-acosamine based on the stereoselective nitro-aldol reaction of 2-O-benzyl-L-lactaldehyde with 3-nitropropanal dimethyl acetal as shovm in Scheme 3 10 The stereoselecdve nitro-aldol reacdon is carried ont by the silyl nitronate approach as discussed in Secdon 3 3... 

Dyong and Bendlin52 pointed out the possibility of functionalization of sorbic acid at C-3, -4, and -5 in the desired way. Introduction of two hydroxyl groups, at CA and C-5, may be accomplished stereospecifi-cally by means of cis-hvdroxylation, or by intermediation of an epoxide. Michael-type addition of a nucleophile to C-3 of the conjugated double-bond provides the possibility of obtaining all four diastereo-isomeric products. In this way, N-acetyl-DL-acosamine (137, 3-acet-amido-2,3,6-trideoxy-DL-arabmo-hexopyranose) was synthesized from 133 (obtained from the epoxide 129 in an aluminum chloride-catalyzed reaction with acetone). The amide 134 wasN-acetylated and... 

Examples for the use of acetals such as 3, of 3-nitropropanal (1), and of 3-nitropropanol (2) or its O-protected derivatives are given in the references.22-24 A recent, notable application from this group is a short, high-yield synthesis of l-acosamine,25 the arabino isomer of 3-amino-2,3,6-trideoxyhexoses that form part of many antitumor aminoglycoside antibiotics 26... 

An intramolecular [3 + 2] nitrone cycloaddition reaction has been employed in the chiral assembly of L-acosamine and L-daunosamine (81JA3956). Heating the masked aldehyde (503) with the oxalate salt of (-)-(S)-7V-hydroxy-a-methylbenzenemethanamine generated a nitrone which underwent intramolecular cycloaddition to give an 82 18 mixture of diastereomers (504) and (505). The N—O bond of the major isomer was cleaved with zinc... 

Heyns et al. [53] started with di-O-acetyl-L-rhamnal (28) which after reaction with sodium azide in the presence of boron trifluoride etherate as Lewis catalyst gave again the four products 79-82 (R=Ac). Subsequent quenching with NIS and the aglycone led to ristosamine and acosamine glycosides 86 and 87. 

The first asymmetric total synthesis of acosamine and daunosamine starting from nonsugar precursor was reported by Fuganti and coworkers [97]. They found that baker s yeast catalyzes the... 

SCHEME 13.52 Fuganti s synthesis of A -trifluoroacetyl-L-acosamine. Copyright 2006 by Taylor Francis Group LLC... 

A simple, divergent, asymmetric synthesis of the four stereoisomers of the 3-amino-2,3,6-trideoxy-L-hexose family was proposed by Dai and coworkers [222], which is based on the Katsuki-Sharpless asymmetric epoxidation of allylic alcohols (Scheme 13.115). Recently, A-trifluoroacetyl-L-daunosamine, A-trifluoroacetyl-L-acosamine, A-benzoyl-D-acosamine and A-benzoyl-D-nistosamine were derived from methyl sorbate via the methyl 4,5-epoxy-( -hex-2-enoates obtained via a chemoenzymatic method [223]. 

The first asymmetric total synthesis of acosamine and daunosamine starting from a nonsugar precursor was reported by Fuganti and co-workers [288,289,290,291]. They found that baker s yeast catalyzes the asymmetric pinacolic cross-coupling of cinnamaldehyde and ethenal giving a ft-diol 156. This diol is protected as an acetonide and submitted to ozonolysis giving L-157. Olefination of L-157 with PhsP = CHCOOMe, followed by treatment with ammonia, provides 158 that is then converted into W-trifluoroacetylacosamine 158 (O Scheme 61). 

Xylitol has been derived from the product of photo-oxidation of cyclopentadiene [484] which is (Z)-(4i 5)-4,5-epoxypent-2-enal. An elegant total synthesis of acosamine and of daunosamine (13 steps, 15% overall yield) was developed at Roche starting from cyclopentadiene [485], The key-step is the asymmetric monohydroboration of 5-methylcyclopentadiene with (—)-di-3-pinanylborane. 

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