Question

write a mechanism for the following procedure

opening directly above the flask and flame-dry the ensemble. At rt, add 2.0 mmoles of the appropriate N-protected amino acid to the flask, followed by 1.05 equivalents of L-alanine methyl ester hydrochloride, 4 mmoles of triethyl amine and 30 mL of anhydrous DMF, the latter two via syringe. After stirring for 5 min, quickly add 1.05 equivalents of TBTU and allow this mixture to stir at rt for 2 hr Add the reaction mixture into a separatory funnel containing 200 mL of EtOAc. Wash the mixture twice with 100 mL portions of 1N HCl and twice with 100 mL portions of 1MKHCO3, and twice with 100 mL water. Dry the organic layer over anhydrous MgSO4, filter and then remove the solvent on the rotary evaporator. Leave the crude product over night for crystallization. The crude dipeptide should crystallize, but if it remains an oil, you may need to triturate the oil with diethyl ether to begin the crystallization process. Obtain a 300 MHz NMR of the crude product to determine the presence of any isomerization product. Expand the relevant range of the NMR spectrum so that peaks due to the a methyl groups are visible so that the ratio of diastereomers may be determined.

Answer 1

The given procedure accounts for synthesis of a dipeptide using TBTU as the activating and coupling reagent.

The mechanism is as follows:

PHN, cOOH 1.4 mmol of TEA 08 PHN. HCI PHN. Me оме YoMe NH2 HCI DMF (solvent) TBTU (coupling agent) е н N-protected amino acid CIH HAN дон L-alanine methyl ester hydrochloride ZI Mechanism PHN. Ņ=N activation PHN. Et N Y OME NH, HCI T Y OMe NH2 O NON coupling PHN - N - 1 YoMe PHN OME IZ NH2