Synthesis ofNeolacto Ganglioside LM1

Abstract

The synthesis of the ganglioside LM1 (1) has been performed by glycosidation of 2 with azidosphingosine 3, followed by reduction of the azido group, acylation with stearine anhydride (4), and solvolysis. 2 was obtained from sialyl xanthate 5 and tetrasaccharide 6 in the presence of phenylsulfenyl triflate. The tetrasaccharide acceptor 6 was prepared from the lactose derivatives 7 and 8.

Hetero-Diels-Alder Cycloadditions ofα,β-Unsaturated Acyl Cyanides, Part 4, Substituent Effects in Reactions withp-Substituted Styrenes

“…The cycloaddition rate is enhanced by the presence of an electron-withdrawing substituent in the heterodiene system, lowering its LUMO and HOMO energy, as well as by an electron-donating substituent in the dienophile system raising its HOMO and LUMO energy. Recent MP2/6-31 G* calculations confirm that the LUMO energy of 2-oxobut-3-enenitrile is much lower than that of acrylaldehyde [17]. Our findings are in agreement with these theoretical expectations.…”

“…13 C-NMR (CDCl 3 ): 158.9 (C(4')); 131.2 (C(1')); 129.0 (C(6)); 126.8 (CH(3'), CH(5')); 116.7 (C(5)); 114.4 (CN ); 113.2 (CH(2'), CH(6')); 77.8 (C(2)); 54.4 ( MeO ); 27.6 (C(3)); 20.9 (C(4)). EI-MS: 216 (17, [ M H] ), 215 (15, M ), 187 (1), 161 (2), 159 (3), 135 (14), 134 (100), 119 (22), 115 (4), 103 (3), 102 (2), 92 (6), 91 (28), 89 (6), 78 (6), 77 (16), 65 (17), 64 (5), 63 (10), 55 (5), 51 (11).…”

“…c-10a/t-10a b 98 :`2: IR (neat):3070m, 3040m, 2232s, 1735vs, 1645vs, 1498m, 1453s, 1370s, 1295vs, 1253vs, 1185vs, 1150vs, 1052vs, 1025vs, 968s, 950s, 903s, 758vs, 700vs. EI-MS: 258 (4, [ M H] ), 257 (6, M ), 185(14), 184(18), 129(11), 128 (9), 115(5), 104 (100), 91(17), 78(12), 77 (16), 65 (4), 51(11).Data of c-10a (from c/t-10a b 98 :`2): 1 H-NMR (CDCl 3 ): 7.38 (m, C 6 H 5 ); 5.90 (dd, J 2.5, 1.9, HÀC(5)); 4.99 (dd, J 11.3, 2.0, H a ÀC(2)); 4.18 (q, J 7.1, MeCH 2 O );3.56 (ddd, J 11.3, 6.3, 2.5, H a ÀC(4)); 2.46 (dddd, J 14.1, 6.3, 2.0, 1.9, H a ÀC(3)); 2.17(dt, J 14.1, 11.3, H b ÀC(3)); 1.28 (t, J 7.1, MeCH 2 O ).13 C-NMR (CDCl 3 ): 170.1 (CO ); 138.3 (C ( Ph)); 130.2 (C(6)); 128.4 (2 CH ( Ph)); 128.2 (CH ( Ph)); 125.7 (2 CH ( Ph)); 113.9 (CN ); 113.7 (C(5)); 78.4 (C(2)); 61.3 ( MeCH 2 O ); 38.5 (C(4)); 31.4 (C(3)); 13.8 ( MeCH 2 O ). Data of Pure t-10a: M.p.…”

Recent developments in oligosaccharide synthesis

“…171 PhSOTf activated sialylation using xanthate donors gave high α-selectivities in the synthesis of a 1C-13 C labelled GM ganglioside 172 and in pentasaccharide ganglioside LM1 due to solvent participation by acetonitrile. 173 An N-glycolylneuraminic acid thioglycoside was used to synthesize a sea cucumber disaccharide ganglioside analogue from a protected Scheme 22 starfish cerebroside with α-selectivity. 174 In a tour de force of protecting group and glycosylation chemistry, the hexasaccharide glycopeptide 63 has been convergently constructed using an initial thioglycoside sialyl donor and trichloroacetimidate glycosides for block assembly via the key divergent lactone intermediate 64.…”

Switchable Diastereoselectivity in Enantioselective [4+2] Cycloadditions with Simple Olefins by Asymmetric Binary Acid Catalysis

“…[4] A straightforward approach to access this type of products is the catalytic asymmetric inverse-electron-demand Diels-Alder reaction between a,b-unsaturated carbonyl compounds and alkenes. [5][6][7][8] Though extensively explored in asymmetric catalysis, [9] this reaction has been limited to electron-rich alkenes, such as enol ethers, enamines, and cyclopentadienes. [10] Reactions with electronically unbiased simple alkenes would give the illustrated compounds directly (Figure 1), but have been rather unsuccessful.…”