Rhamnales

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). 

Stamens opposite the petals or if apetalous alternate with the sepals.Order Rhamnales... 

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... 

When 3,4-di-O-benzyl-D-rhamnal is reacted with methyl a-D-evermicoside by the glycosyloxy-selenenylation procedure (phenylselenenyl chloride, acetonitrile,. vy/w-collidine, 1 h) 1, 2 -trans-diaxial (1-3) linked disaccharide 20 is obtained in 70% yield31. 

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