Recently, 4,6-dideoxy-4-N-formamido-3-C-methyl-2-O-methyl-L-mannose (l), an N-substituted derivative of kansosamine, was reported' as the non-reducing terminus of the type-specific pentasaccharide determinant of serovariant 14 of the Mycobacterium auium complex. Two other naturally occurring derivatives of 4-amino-4,6dideoxy-3-C-methyl+mannose have been reported, namely N-
from Mycobacterium kansasii2~3 and L-sibirosamine (4,6-dideoxy-3-C-methyl-4-methylamino-L-mannopyranose)
from Streptosporangium sibiri-cum4*'.
In connection with the synthesis of the pentasaccharide antigen of serovariant 14 of the M. auium complex, we now report the title compound, which is a C-l-activated derivative (10) of N-formylkansosamine.
Oxidation of phenyl 6-deoxy-2,3-0-isopropylidene-1 -thio-cr-L-mannopyrano-side6 (2) by pyridinium chlorochromate in dichloromethane gave 70% of the ulose 3, but no sulphoxide or sulphone. Generation of the carbanion of 3 was achieved with lithium di-isopropylamide and treatment with methyl iodide proceeded with low stereoselectivity, and only 56% of the desired axial 3-C-methyl derivative 4 could be isolated. Treatment of 4 with 10 equiv. of hydroxylamine hydrochloride-sodium carbonate in ethanol at 90" afforded 60% of the oxime 5, reduction of which with 10 equiv. of lithium aluminium hydride in oxolane gave a -1:l mixture of the L-manno (6) and L-tale amines. Only 6 was isolated (30%) and was treated in dichloromethane with carbodiimide-formic acid to yield 7 (70%). The proton of the formyl group resonated at 8.04 and 8.24 p.p.m_, reflecting the two environments caused by hindered rotation around the formyl C-N bond. Removal of the isopropylidene group from 7 gave a diol, attempted selective methylation of which resulted in both 0-and N-methylation.
l Dedicated to Professor Leslie Hough in the year of his 65th birthday.