DesVI: A New Member of the SugarN,N-Dimethyltransferase Family Involved in the Biosynthesis of Desosamine

Abstract

Methylation catalyzed by S-adenosylmethionine (AdoMet) dependent enzymes is one of the most common reactions occurring in biological systems. While a large number of methyltransferases which catalyze methylation at carbon, instead, presumably by means of b-H elimination. [7] As shown also in Scheme 3, activation of EtOPh by 1 (toluene, 110 8C, 2 h) gave compound 6 (see Supporting Information). It thus appears that the very important steric demands of the Tp x ligand (as compared with the somewhat less bulky cyclopentadienyl ligand, Cp x ) and its rigid nature, which tends to enforce six-fold coordination to the metal center, favors a-H elimination over b-H elimination in the transformations studied here.In summary, we have shown that the Ir I compound 1 effects the regioselective, double CÀH activation of a variety of ether and amine substrates by allowing their precoordination to the metal center. The formation of Fischer-type carbenes in this cascade activation (cyclometalation-b-elimination (or vice versa)-a-elimination) is made possible by the presence of an adequate hydrogen-accepting leaving group. The Tp x -and Cp x -Ir systems reported herein include O and N heteroatoms. Comparative studies on the facility of these fundamental organometallic reactions (a-and b-eliminations) on closely related Tp x -and Cp x -Ir systems without these heteroatoms that could alter the relative energies of the transition states and intermediates, [17] are presently in progress and will be reported in due course. Experimental Section1: To a suspension of [(IrCl(coe) 2 ) 2 ] (175 mg, 0.20 mmol) in CH 2 Cl 2 (6 mL), 2-methylbutadiene (0.3 mL, excess) was added at room temperature to give a colorless solution. A solution of TlTp Ph (253 mg, 0.40 mmol) in CH 2 Cl 2 (6 mL) was then added. Stirring the reaction mixture for 4 h at room temperature resulted in the precipitation of TlCl. After filtration, the clear solution was evaporated to dryness. The crude product (orange powder) was purified via column chromatography (neutral aluminum oxide 90 % activated, eluents PE (petroleumether):Et 2 O 15:1, eluted as a pale violet band). Compound 1 was obtained upon changing the eluents to PE:Et 2 O 4:1 and it eluted as a yellow band. Removing the solvent and drying in vacuum gave pure 1. Yield: 198 mg (71 %). Elemental analysis: calcd for C 32 H 30 BIrN 6 (%) : C 54.8, H 4.3, N 12.0; found: C 54.4, H 4.1, N 12.2. Compounds 2 ± 6 can be prepared similarly by treating 1 with an excess of the corresponding ether or amine. As a representative example the synthesis of 5 is given: A solution of 1 (70 mg, 0.10 mmol) in Et 2 O was heated at 60 8C for 12 h. The solution was evaporated to dryness. Purification by flash chromatography (neutral aluminum oxide 90 % activated, eluents PE:Et 2 O 2:1, eluted as a yellow band) resulted in pure 5. Yield: 58 mg (82 %). Elemental analysis: calcd for C 31 H 30 BIrN 6 O (%): C 52.[1] a)

Nucleotide Deoxysugars: Essential Tools for the Glycosylation Engineering of Novel Bioactive Compounds

“…dTDP-β-L-epivancosamine (dTDP-3-amino-2,3,6-trideoxy-3-C-methyl-β-L-arabino-hexose) (128) [123] and [155] dTDP-α-D-desosamine (dTDP-3-N,N-dimethylamino-3,4,6-trideoxy-α-D-glucose) (6) WW 3 8.3 144 [154] and [36] dTDP-4,4-difluoro-2,4,6-trideoxy-α-D-glucose (129) 1 dTDP-α-D-desosamine (dTDP-3-N,N-dimethylamino-3,4,6-trideoxy-α-D-glucose (6) --->80 a [36] dTDP-6-deoxy-4-keto-α-Dglucose ( 14) 2 dTDP-3-amino-2,3,6-trideoxy-4-keto-α-Dglucose ( 138) 0.86 30 b [32] dTDP-6-deoxy-4-keto-α-Dglucose ( 14)…”

“…The dTDP-3-amino-3,4,6-trideoxy-α-Dglucose (100) was synthesized chemically as a substrate for the enzymatic synthesis of 6 by the methyltransferase DesVI (see chapter 2.4.2) [36,153,154]. Two different routes were realized forming the unprotected aminosugar phosphate after 10 steps.…”

“…(27) and Tab. 7 [36,154]. Desosamine was obtained by hydrolysis of erythromycin B (133) and directly acetylated to form 134 and a yield of 89% was achieved.…”

“…After isolation by gel filtration and anion exchange chromatography 144 mg (257 µmol) of 6 were obtained corresponding to an overall yield of 8.3% [36,154].…”

“…The first short activation pathway was recognized for L-fucose [157,158], which is normally synthesized from GDP-D-mannose (171) by the standard dTDP-α-D-desosamine (6) was synthesized by enzymatic methods using DesVI (Tab. 8) [36,154] nucleophilicity of an amino sugar. It also causes a significant change in size, hydrogen bonding capacity and propensity for protonation of the substrate´s amino groups.…”