L-Rhamnal

SCHEME 9. Ferrier rearrangement by glycosidation of 3,4-di-O-acetyl-L-rhamnal with several alcohols catalyzed by Montmorillonite K-10. 

As the precursor for the B unit, the selectively benzylated -fucal derivative 75- could be obtained crystalline from L-fucal by applying a phase-transfer-catalyzed process T64). By a Ferrier reaction of di-O-acetyl-L-rhamnal and a subsequent retro enol ether formation trough hydride attack at C-3 (71.) the -amicetal 72 was obtained (64) this reaction was concurrently also es-cribed by others (72). 

Micheel220 obtained 5-deoxy-L-arabinose and -D-ribose derivatives by the oxidation of L-rhamnal and 6-deoxy-D-allal derivatives, respectively, with ozone. 

The reagent reacts selectively with the allylic hydroxyl group of 6-deoxyglycals 95 % of 3-0-(/ert-butyldimethylsilyl)-L-rhamnal were isolated after 2 h reaction at room temperature, in addition to 3 % of the 4-silyl and 2 % of 3,4-disilyl ethers [424]. Reinvestigation of this reaction by Thiem and coworkers revealed that temperatures below —20 °C are necessary in order to achieve such a high regioselectivity. At room temperature, a complicated mixture of products was obtained [127a]. Derivatives of N-acetylneuraminic acid such as 59 were also partially silylated with efficiency... 

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. 

Also 2 -halo-3 -hydroxy derivatives of various anthracyclinones show a high activity against P 388 mouse leukemia in certain in-vivo tests. A compound like 98 has been prepared in the 2-deoxy-2-iodo-a-L-ma no-series by Horton et al. [59, 60] starting from di-O-acetyl-L-rhamnal (28). Similarly, Thiem et al. have also successfully prepared the tetracenomycinone-C glycoside 99 [61]. From 4-0-acetyl-3-0-(p-methoxy)-benzyl-L-fucal (102) the glycoside derivatives 103 and 104 in the talo-series were obtained. 

By Ferrier glycosylation of di-O-acetyl-L-rhamnal (28) with the epoxide derivative 117 the disaccharide 118 is obtained. This is trans-opened by lithium iodide according to Fiirst-Plattner s rule. Upon different ways, two interesting products are obtained, either the original C-B disaccharide of aclacinomycin A 120 or its C-5 epimer 119 which contains one sugar in the D-configuration [69]. 

A sulfonic acid resin (AG-50W X8) in the presence of lithium bromide was used under anhydrous conditions to promote the acidic addition of alcohols to glycals (Scheme 6). a-Stereoselectivity was observed for D-glucal, L-glucal, and L-rhamnal.34... 

The d- and L-enanatiomers of rhodinose and amicetose specifically labeled with deuterium at C-2 and C-3 were prepared from the same synthon.274 Starting from 3,4-di-O-acetyl-L-rhamnal, (2S,3f )-[2,3-2H2]-L-rhodinosc was synthesized as shown in Scheme 58. 

On one hand, the a,P-unsaturated lactone 40, which was derived from di-O-acetyl-L-rhamnal (39) according to reported procedures, was submitted to Mitsunobu inversion with HCO2H, followed by hydrolysis and methoxymethylation to afford 40. On the other hand, the o-methylbenzoate 41 was obtained from 3,5-dihydroxytoluene under the protocols described by Solladig. 

D-glucal, an acetyl group is removed from diacetyl-L-rhamnal by boiling its aqueous solution. The resulting monoacetyl-L-pseudorhamnal, however, is not as stable as diacetyl-D-pseudoglucal.7 Oxidation of diacetyl-L-rhamnal with ozone yielded 5-desoxy-L-arabinose, which was characterized as its phenylosazone and p-bromophenylosazone. 7 Deacetylation of diacetyl-L-rhamnal yields crystalline L-rhamnal (XLIV).7... 

Addition of halogens produces dihalides, of which, for example, a dibromide crystallizes easily but is very unstable.7 Perbenzoic acid oxidizes L-rhamnal to L-rhamnose.7 The primary oxidation product, probably an epoxide, upon treatment with anhydrous methanol gives methyl diacetyl-a-L-rhamnoside.38 Crystalline 2-desoxy-L-rhamnose was prepared from L-rhamnal.18-3 ... 

L-Rhamnal (155) Acetal CH2C12 Et3N Amb. Benzoyl chloride — 78 0 286... 

In order to confirm this conclusion, both D- and L-arabomethylose, which would give the same osazones as d- and L-ribomethylose, were prepared by ozonization of D- and L-rhamnal. Physical constants of derivatives of all pentomethyloses concerned in the argument are shown in Table III. From these data, as well as from mixed melting point... 

For example, treatment of di-O-acetyl-L-rhamnal 26 with silylated pyrimidine or purine bases in the presence of a mild acidic catalyst (trityl perchlorate) afforded 2,3-unsaturated pyra-nosyl nucleosides, as a mixture of a,/3-anomers 27 (with the / -anomer predominating) [37]... 

Further support for the HS AB-based rationalization comes also from later studies demonstrating that making sulfur harder (5 -alkyl to S-acetyl) dramatically alters regioselectivity and leads to 2,3-unsaturated products [176,177]. In the reaction from 3,4-di-O-acetyl-L-rhamnal 87 with thioacetic acid or potassium thioacetate in the presence of BF3 -Et20, only products substituted at C-1 88 and 89 were isolated (O Scheme 30) [177]. 

Syntheses of Daunosamlne and its Isomers - Three syntheses of the natural L-antipode of daunosamlne ( ) have been recorded. The first, by Goodman and colleagues, commences with L-rhamnal (90) and proceeds as shown in Eq.4. A second, due to Yamaguchl and Kojlma begins with 9 (from glu-... 

In other work, methoxymercuration has been applied in the first stage of the synthesis of L-daunosamine (14). Methoxymercuration of L-rhamnal (15), followed by reduction of the carbon-mercury bond with potassium borohydride, afforded30 a route to methyl 2,6-dideoxy-a-L-arafcmo-hexopyranoside (16), the enantiomorph of methyl chromoside C. 

D-glucal, D-galactal, L-rhamnal, cellobial, lactal, maltal... 

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