Shaka-ROESY ‘n’ friends: Shaka-ROESY ‘n’ friends Brent Riffel Brett Shapiro Chem 172 May 7, 2002 Brent Riffel & Brett Shapiro May 7, 2002


The Big Picture: The Big Picture Who: Erythromycin Enol Ether What: Assign NOEs between protons Why: Elucidate 3D Structure How: NOE Difference Spectrum GOESY New Shaka-ROESY


Erythromycin Enol Ether: Erythromycin Enol Ether Antibiotic metabolite From Erythromycin A Diarrhea, Flatulence Structure Two sugar rings Lactone ring Examine 1" proton


Preliminary 3D Conformation: Preliminary 3D Conformation Prior Research: Preliminary structure from ROESY data (SYBYL) Current Project: Examine 1'' proton & protons in spatial proximity 1"


ROESY and Shaka-ROESY: ROESY and Shaka-ROESY ROESY Peak phase independent of τc Traps magnetization about y-axis using spin-lock Problems: COSY contamination from antiphase magnetization TOCSY contamination when Hartmann-Hahn condition met Shaka-ROESY Advanced pulse sequence suppresses TOCSY contamination


Shaka-ROESY: Shaka-ROESY


Zoom in on Shaka-ROESY!: Zoom in on Shaka-ROESY!


Nuclear Overhauser Effect: Nuclear Overhauser Effect NOE caused by dipole-dipole relaxation Relevant parameters: are T1 and τc Double quantum (2Q) & zero quantum (0Q) transitions allowed in relaxation


NOE Difference Experiment: NOE Difference Experiment Irradiate to saturate proton’s magnetic transitions Baseball bat (!!!) System seeks equilibrium (0Q & 2Q transitions) NOE diff. Spectrum irradiated MINUS control Negative peak corresponds to proton of interest Positive peaks indicate NOE Subtraction artifacts Peaks are dependent on τc


Slide11: Theoretical Erythromycin Enol Ether


GOESY Theory 1: GOESY Theory 1 GOESY = Gradient Enhanced Overhauser Spectroscopy NO subtraction artifacts ½ S/N ratio as NOESY, but more than com-pensates b/c no subtraction artifacts Detect NOE enhancements < 0.1% Comparison of GOESY and NOE Difference Spectra for Progesterone. Adapted from J. Am. Chem. Soc., Vol. 117, No. 14, 1995.


GOESY Theory II: GOESY Theory II G1 and G2 adjusted to exactly defocus and refocus the magnetization Gm eliminates all but wanted z-magnetization Peaks in spectrum: Protons selectively irradiated Nearby protons experiencing cross-relaxation GOESY Pulse Sequence: 90º(x, sel)-G1-90º(x)-τm-Gm-90º(x)-τ2-180º(x)-G2-acq


GOESY and NOE diff. Compared: GOESY and NOE diff. Compared Proton Spectrum GOESY Spectrum NOE diff. Spectrum


Zoom in on GOESY!: Zoom in on GOESY! Proton Spectrum (expansion) GOESY Spectrum (expansion) GOESY Spectrum (full)


Problems with GOESY: Problems with GOESY Can have zero-q coherence Caused by 2nd 90º(x) pulse Cannot be separated from wanted z-magnetization Appears in spectrum antiphase 90º(x, sel)-G1-90º(x)-τm-Gm-90º(x)-τ2-180º(x)-G2-acq Original GOESY Pulse Sequence: Pulse sequence developed by the SHAKA group to suppress antiphase contributions


Compare to 3D Preliminary Conformation: Compare to 3D Preliminary Conformation 1" 2"eq 4" 3"OMe 2"ax 3 2Me