Acylation of amino alcohol (I) with (R)-3-(n-tetradecanoyloxy)tetradecanoic acid (II) employing 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide methiodide (EDC.MeI) provided amide (III). After hydroxyl group protection with 2,2,2-trichloroethyl chloroformate (A), the resulting acetonide (IV) was hydrolyzed with aqueous AcOH to give (V).
N-Protection of amino alcohol (VI) under Schotten-Baumann conditions with 2,2,2-trichloroethyl chloroformate (B) aforded carbamate (VII). Subsequent esterification of (VII) with acid (II) provided (VIII), which was followed by acetonide hydrolysis to give diol (IX). Selective protection of the primary hydroxyl of (IX) with 1,1-dimethyl-2,2,2-trichloroethyl chloroformate (C) furnished carbonate (X). Further phosphorylation of the free secondary hydroxyl of (X) with diphenylphosphoryl chloride (D) produced phosphate ester (XI). Conversion of the trimethylsily-ethyl glycoside (XI) into the desired glycosyl chloride (XII) was then accomplished by treatment with alpha,alpha-dichloromethyl methyl ether and ZnCl2.
Coupling of glycosyl chloride (XII) with glycoside (V) in the presence of silver triflate gave rise to the corresponding beta-disaccharide and subsequent reductive cleavage of the trichloro ethyl-based protecting groups with Zn/AcOH yielded disaccharide (XIII). Further N-acylation of (XIII) with acid (II) in the presence of 2-ethoxy-1-(ethoxycarbonyl)-1,2-dihydroquinoline (EEDQ) furnished amide (XIV). Finally, two-step hydrogenolytic deprotection of the benzyl and phenyl groups of (XIV) and lyophilization in the presence of triethylamine provided the title compound.
In a related procedure for the synthesis of the protected precursor (XIV), the known bis(trichloroethoxycarbonyl) derivative (XV) was coupled with glycosyl chloride (XII) to give the corresponding disaccharide which was deprotected to (XVI) upon treatment with Zn/AcOH. Bis N-acylation of (XV) with acid (II) in the presence of EEDQ then provided the target intermediate (XIV).