Cyclodextrin derivatives in gas chromatographic separation of racemates with different volatility. Part XV: 6-O-t-butyldimethylsilyl- versus 6-O-t-hexyldimethylsilyl-? and -? derivatives

Cyclodextrin derivatives in GC separation of racemates of different volatility Part XVIII: 2-methyl-3-acetyl- and 2-acetyl-3-methyl-6-O-t-hexyldimethylsilyl-γ-cyclodextrin derivatives

“…ME-THDMS-and AC-THDMS-c-CD were synthesised in a two-step reaction following the method described by Takeo [12,13] and Mosandl [14] and modified in the authors' laboratory [15,16]. All details and spectroscopic data are reported elsewhere [11].…”

“…Their results were compared with those of CDs in which the same substituent (i. e. ME and AC) is introduced in positions 2 and 3 of the CD ring. The CD substituents were chosen on the basis of derivatives that were previously shown to be successful as enantioselective stationary phases [11]. The performance of the following four CD derivatives were compared: 2,3-ME-THDMS-c-CD, 2-ME-3-AC-THDMS-c-CD, 2-AC-3-ME-THDMS-c-CD and 2,3-AC-THDMS-c-CD.…”

“…Pesticides were chosen because they are generally medium-to-low-volatility compounds and contain heteroatoms in their structures. In this case 2,3-AC-THDMS-c-CD is the derivative showing the highest enantioselectivity, while, as reported elsewhere [11], 2,3-ME-THDMS-c-CD enantioselectivity with the compounds investigated was extremely low since only propargite was separated and not at the baseline (R : 1.0). 2-AC-3-ME-THDMS-c-CD and 2-ME-3-AC-THDMSc-CD have lower enantioselectivity than 2,3-AC-THDMSc-CD.…”

“…In a previous article [11], the role played by the bulky groups t-hexyldimethylsilyl-(THDMS) and t-butyldimethylsilyl-(TBDMS) introduced in position 6 of b-and c-CD was studied by comparing the performance of columns prepared with 2,3-di-O-methyl-(2,3-di-ME-), 2,3-di-O-ethyl-(2,3-di-ET-), and 2,3-di-O-acetyl-(2,3-di-AC-) derivatives by analysing a series of medium-to-high volatility racemates and one of medium-to-low volatility chiral pesticides. These experiments indicated that the enantioselectivity of the investigated CDs was conditioned by the volatility, size, and polarity of the racemates analysed: with medium-to-high volatility racemates, the TBDMS-bCDs were the most enantioselective, while the THDMS-cCDs had a comparable or better enantioselectivity than the corresponding TBDMS-b-CDs with medium-to-low volatility racemates.…”

“…These experiments indicated that the enantioselectivity of the investigated CDs was conditioned by the volatility, size, and polarity of the racemates analysed: with medium-to-high volatility racemates, the TBDMS-bCDs were the most enantioselective, while the THDMS-cCDs had a comparable or better enantioselectivity than the corresponding TBDMS-b-CDs with medium-to-low volatility racemates. 6-TBDMS-or 6-THDMS-b-and c-CDs substituted in positions 2 and 3 with methyl or acetyl groups are among the most effective derivatives used as chiral selectors for enantioselective GC [7,11] and show enantioselectivities that very often are complementary. 2-ME-3-AC-and 2-AC-3-ME-6-THDMS-c-CDs were synthesised and tested as GC stationary phases, with the aim of developing CDs of as universal as possible application, and of evaluating how the simultaneous introduction of ME and AC groups in positions 2 and 3 of the CD ring influences enantioselectivity.…”