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17th January 2012 @ 04:21
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Boc-deprotection of PMY 29-2-A using anhydrous hydrogen chloride.

Reaction Scheme

Reaction Start time: 14.30 17/01/12
PMY 29-2-B (240 mg, 0.67 mmol, 1 equiv.) was stirred in toluene (5 mL) in a water/ice bath. Partial solution/mostly suspension. 4M HCl in dioxane (0.35 mL, 1.4 mmol, 2.1 equiv.) was added. In less than 1 minute, slightly purple precipitate forms. TLC (mini-work up; solid dissolved in water, NaHCO3 added followed by acetone.) shows consumption of starting material and a new very polar spot. Reaction was extracted with water (3 × 5 mL). NaHCO3 was added to the aqueous layer whereupon the colour changed from pink to yellow. The basic solution was extracted with DCM (3 × 5 mL). The organic extracts were dried (MgSO4) and concentrated under reduced pressure to obtain a yellow powder (52 mg), PMY 30-2-A. 1H NMR is consistent with starting material. The toluene layer, and aqueous layers were combined and acidified with conc. HCl and left overnight, PMY 30-2-B. The recovered SM, PMY 30-2-A, was dissolved in diethyl ether and 4M HCl in dioxane (0.5 mL) was added. A precipitate forms immediately. The mixture was left overnight. Solvent had evaporated from PMY 30-2-A overnight leaving concentrated aqueous solution which was diluted with further water. Both -A and -B were analysed by TLC then basified (pH 10) by addition of solid Na2CO3. Re-TLC'd showing some very polar product spot by UV (slight movement up the plate only). PMY 30-2-B was then concentrated under reduced pressure. The residue was stirred with MeOH (50 mL) and filtered. The filtrate was concentrated under reduced pressure. 1H NMR not consistent with expected product. Mass spec is consistent with expected product.

TLC (10% MeOH/DCM) visualised with UV and vanillin:
TLC of PMY 30-2-A and -B at pH 10
TLC of PMY 30-2-A and -B at pH 1

TLC of SM, PMY 30-2-A and PMY 30-2-B after further acid treatment (left) and then basified (right).

NMR:
1H NMR crude
1H NMR aqueous


Mass Spec:
PMY 30-2-B Mass Spec

m/z] (ESI+) 283 [M+Na]+, 100%.

See also:
Deprotection of Boc-Gly-4-aminoantipyrine (PMY 30-1)

Risk and Hazard Assessment:
RA
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Attached Files
RA
Scheme
1H NMR crude
TLC of PMY 30-2-A and -B at pH 1
TLC of PMY 30-2-A and -B at pH 10
1H NMR crude
1H NMR aqueous
PMY 30-2-B Mass Spec
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