2. Horner-Wittig Reagents in Sulfur and Selenium Chemistry Pieter Otten and Arne van der Gen Leiden Institute of Chemistry Leiden University, The Netherlands P S Se

4. Thioamide Synthesis Aminomethylphosphine oxides, excellent reagents for enamine formation, show a unique reactivity towards chalcogens to form amides R = aryl: reaction at r.t R = alkyl: reaction at 0 o C to quell deprotonation of formed thioalkanamides by the HW reagent

5. Selenoamide Synthesis “ Red selenium”, Se 8 , more reactive than metallic or gray Se; allows isolation of acidic selenoalkanamides at lower temperatures Reaction is sluggish at ambient.

6. Mechanistic Considerations One eq. of S gives < 50% yield, recover phosphine oxide All intermediates isolated and characterized. Mass balance accounted for. Intermediate trapped at low temperatures with MeI Independently confirmed

7. Crystal Structure Selenobenzamides Amino group reduces dihedral angle  C=Se: 1.840 Å C-N: 1.331 Å  = 53.3º C=Se: 1.824 Å  = 81.1º C(5) is sp 2 -hydrid.

8. Other Selenocarbonyls C=Se of selenoamides close to other N- or C=C-conjugated selenocarbonyls

9. VT 13 C NMR Study: Rotational Barriers C=S and C=Se strongly e-withdrawing groups,  + p fits only More polarizable Se more sensitive to  + p than S o = Se * = S Eyring eq.:  G* rot = 19.5T c x [9.971 + log(T c /  )]

10. Synthesis of (Thiomethyl)- and (Selenomethyl)phosphine Oxides

12. Mechanistic Considerations (Curtin-Hammett Principle) Trapped HW-adducts (R3 = Ph -60 o C, H 2 O): R1 = n-Pr: pro(E)/pro(Z) = 1/1, quant. R1 = c-Hex: pro(E)/pro(Z) = 1/1+ 22% (E)-vinyl selenide! Sterics facilitate elimination, k E increases R1 = phenyl, pro(E)/pro(Z) = 3/2. quant, pro-(E) and pro(Z) must rapidly equilibrate via reverse to aldehyde and/or epimerization and (E)-isomer is thermodynamic sink pro-(E) Pro-(Z)

13. Do HW adducts equilibrate? No vinyl selenide derived from propionaldehyde observed: no equilibration via reverse reaction with aliphatic aldehydes. Cannot rule out epimerization. Fast equilibration with aromatic aldehydes to explain discrepancy between pro-(E) and pro-(Z) ratio for isolated HW adduct (3/2) and strong E-selectivity for completed HW reaction.

14. Alternate Intermediate Warren proposes this late-stage intermediate to explain high pro-(Z) selectivity for simple alkyl phosphine oxides (R1 = alkyl) Pro-(E) Six-centered transition state. R1 equatorial to avoid 1,3-interaction with equatorial Ph. Low energy difference between SeR3 equatorial or axial, reflected by observed low stereoselectivity In HW-adducts. Pro-(Z)

15. Formation of 1-Chlorovinyl Sulfoxides A New Class of Compounds (1994)

16. >96% Z-selectivity if R 2 = aryl, alkenyl and/or R 1 = aryl

17. Crystal Structure Confirms Z-geometry P -1 , a = 13.3146, b = 11.326, c = 9.395 Å;  = 125.15  = 97.88,  = 96.76; V = 1097.45 Å 3 , Z = 4,  = 1.396 kg/dm 3

18. Mechanistic Considerations Phosphine oxide anion and carbonyl are in equilibrium w/ adduct. Fast when R1 = anion stabilizing aryl Rotation sets up for the oxaphosphetane. Sterics favor pro-(Z) intermediate Thermodynamic sink Elimination fast if R2 stabilizes double bond: aryl, vinyl

19. Mechanistic Considerations: Alternate Approach Surprisingly poor stereochemistry with bulky c-hexanecarboxaldehyde Li + ligated between P=O and S=O. R1 equatorial to avoid axial Ph. Aldehyde approaches with R2 pointing away from axial Ph. Must be an intermediate trough on the energy surface

20. Michael Addition P 2 1 , a = 6.371, b = 7.646, c = 12.364 Å;  = 90.0  = 98.45,  = 90.0; V = 595.7 Å 3 , Z = 2,  = 1.50 kg/dm 3

21. Mechanistic Considerations A compact sodium complex is formed, dictating stereochemistry Malonitrile gives 1:1 mixture of diastereoisomers

22. Synthesis of S , N -ketene Acetals and Thioesters R2=aryl: pure ketene acetale after extractive work-up only. R2=alkyl, contaminated w/ condensation products. Carry thru to thioester for good use

24. Fluorescent Magnesium Indicators Pieter Otten, Louis Levy, and Robert London, National Institute of Environmental Health Sciences, RTP, NC

27. Why APTRA (Aminophenol Triacetic Acid)? At physiol. Mg 2+ , BAPTA binds two ions. Cut BAPTA in half to get to APTRA.

28. Pd coupling: fast, one step approach to quickly invest structural diversity

29. Suzuki Coupling K D, Mg = 2.3 mM K D, Ca = 70  M K D, Mg = 2.1 mM K D, Ca = 28  M K D, Mg = 1.8 mM K D, Ca = 17  M

30. Fluorescence Excitation Titration Response to Mg and Ca is not identical, which was often assumed to correct for Ca-spikes

31. Synthesis of 4-Oxo-4 H -quinolizine-3-carboxylates Known complexers of Mg 2+ to shut down bacterial DNA-gyrase w/ K D = 1 mM Explore reactivity to diversify quickly

32. Electrophilic Aromatic Substitution

33. 4-Oxo-4 H -quinolizine-3-carboxylic Acids Compare:

34. Representative Examples; Tri-acids

35. Synthesis Bromo-substituted Triacid Introduce 3 rd ester, as decarboxylation could not be prevented

36. Fluorescence Emission Spectrum The first Mg-selective, ratioable fluorophore!

37. Selected Fluorophores Emission > 500 nm Ratioable

40. NMR-active, Fluorinated Reporter Molecules Pieter Otten and Ralph P. Mason Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX

41. 6-FPOL pK a = 8.2

42. 6-FPAM pK a = 7.05

43. CF 3 -POL Triple the fluorines, triple the signal Does not penetrate rbc membrane

44. Fluorinated Gene Reporter Saline at 30 o C (♦) Plasma at 30 o C (□) Plasma at 37 o C (Δ) Top: pH = 4.5; t = 30 o C; β-gal ( Aspergillus Oryzae ) Bottom: pH = 7.3 -> 6.8; t = 37 o C; β-gal ( E. Coli ) pK a = 6.85