Stereochemical Assingment of β -lactam Antibiotics and their Analogues by Electronic Circular Dichroism Spectroscopy

Synthesis, Separation and Absolute Configuration Determination by ECD Spectroscopy and TDDFT Calculations of 3‐Amino‐β‐lactams and Derived Guanidines

“…However, for small deviations from planarity of the -lactam ring, the helicity rule should not be considered at all. [21,29,30] The comparison between experimental and TDDFT-calculated ECD and absorption spectra is, in all cases, good over the whole wavelength range. It is always recommended in ECD TDDFT calculations to test several different functionals, with special attention towards range-separated functionals such as CAM-B3LYP [33] and ωB97X-D, [34] which generally outperform global hybrids.…”

“…Most importantly, the band allied with the n-π* transition must be identified in the ECD spectrum. [21,25,[27][28][29][30] These findings further demonstrate that a safe ECD absolute configuration determination of -lactams cannot be based exclusively on the sector/helicity rule. The applicability of the sector/helicity rule has been verified for -lactams containing additional aromatic, diene and carbonyl chromophores, [22,25,27,28] and the rule was found to be valid in almost all cases.…”

“…[13] Furthermore, the choice of chiral auxiliary determines efficient methods to assign the absolute configuration of organic chromophoric compounds. [21] Several semiempirical rules have been devised to assign the absolute configuration of -lactams from their ECD spectra. [21] Several semiempirical rules have been devised to assign the absolute configuration of -lactams from their ECD spectra.…”

“…[15][16][17][18][19][20] ECD spectroscopy is the tool of choice to assign the absolute configuration of -lactams, either appended or not with chromophores other than the amide group. [21] Depending on whether the -lactam ring is planar or not, either a sector rule [22][23][24][25] or a helicity rule [21,26,27] should be applied, respectively. They all rely on the ECD band, or Cotton effect (CE), associated with the carbonyl n-π* transition at ca.…”

Synthesis of terminal alkynes based on (1S,3R,4R)- and (1S,3S,4R)-2-azabicyclo[2.2.1]heptane

“…Such approach in stereochemical analysis of chiral compounds has been already recognized to be substantially useful, effective, and steadfast for various chiral molecules, and in many cases it is the complementary part of spectral analysis. [19][20][21][22][23][24][25] In Figure 1 the measured ECD/UV spectra of compound 13 in hexane solution are presented (black line). As can be seen, in the measurement range there are two ECD bands: a minimum at 215 nm, maximum with well-developed fine structure centered at 262 nm, and one shoulder at ca.…”