4,4-dimethyl-2,6-dioxocyclohexylidene methyl

Dimethyl and methyl phenyl 4,4-dimethyl-2,6-dioxocyclohexylidene tellurium compounds transferred a methyl group to triethylamine, triphenylphosphane, tris[di-methylamino]phosphane, and triphenylarsane. The methyl onium cations were isolated as lelraphenylborates. The alkylidene organo telluronium intermediate was identified by 31P-NMR spectroscopy in the reaction of the ylide with tris[dimethylamino]phosphanc . 

The three orthogonally removable lysine protecting groups we use here are Fmoc (9-fluorenyl methoxy carbonyl), cleavable with 20% base, preferably with 20% piperidine or 3% DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) (18), Dde (1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-ethyl), cleavable with 2% hydrazine, and Aloe (allyloxy carbonyl), cleavable with palladium. Hydrazine also removes Fmoc, and thus it can be applied only if no Fmoc groups are present on the growing peptide chain. Acid-sensitive amino protecting groups available are Boc (tert-butyloxy carbonyl), cleavable with 90% TFA, and Mtt (4-methyl-trityl), cleavable with 1% TFA. We use Boc for the protection of the N-terminal moieties of N-terminal amino acids in each peptide chain as well as at the N-terminus of the scaffold. 

The iV-l-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl linker has also been introduced between the C2-amino group of the glucosamine and a solid-support [5]. This linker was stable during glycosylation with thioglycoside in the presence of methyl trifluoromethane sulfonate, but readily cleaved by hydrazine, primary amines, or even ammonia. 

W-(5,5-Dimethyl-3-oxo-l-cyclohexenyl), 833 W-2,7-Dichloro-9-fluorenylmethylene, 833 W-l-(4,4-Dimethyl-2,6-dioxocyclohexylidene)ethyl, 833 W-(l,3-Dimethy-2,4,6-(l//,3//,5//)-trioxopyrimidine-5-ylideny)methyl, 834 W-4,4,4-Trifluoro-3-oxo-l-butenyl, 834 N- (l-Isopropyl-4-nitro-2-oxo-3-pyrrolin-3-yl, 835... 

---