Asymmetric Synthesis of (2S,3S)- and
(2R,3R)-α,β-Dialkyl-α-amino
Acids via Alkylation of Chiral Nickel(II) Complexes of Aliphatic α-Amino
Acids with Racemic α-Alkylbenzyl Bromides

Vadim A. Soloshonok; Thomas U. Boettiger; Shawna B. Bolene

doi:10.1055/s-2008-1067172

PAPER

Asymmetric Synthesis of (2S,3S)- and (2R,3R)-α,β-Dialkyl-α-amino Acids via Alkylation of Chiral Nickel(II) Complexes of Aliphatic α-Amino Acids with Racemic α-Alkylbenzyl Bromides

Vadim A. Soloshonok*, Thomas U. Boettiger, Shawna B. Bolene
Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
Fax: +1(405)3256111; e-Mail: vadim@ou.edu;

Abstract

All articles of this category

Abstract

This study has demonstrated that the stereochemical outcome of the direct alkylation of nickel(II) complexes derived from chiral Schiff bases of glycine, alanine, 2-aminobutyric acid, and leucine with racemic α-methylbenzyl bromide depends on the steric bulk of the corresponding amino acid residue. In particular, the alkylation of the alanine complex was found to proceed with a synthetically useful level (90% de) of stereoselectivity offering a concise synthesis of enantiomerically pure (2S,3S)- or (2R,3R)-α,β-dimethylphenylalanines.

Key words

sterically constrained amino acids - alkylation - asymmetric synthesis - kinetic resolution

Full Text

References

As we recently pointed out (see ref. 2), the terms unnatural, unusual, or nonproteinogenic, noncoded amino acids depend on the success of specific scientific achievements. For instance, amino acids containing the most xenobiotic element fluorine were shown to be synthesized by microorganisms (see ref. 3), and also new amino acids can be added to genetic code of microorganisms (see ref. 4). Therefore, the time-independent term tailor-made, meaning rationally designed/synthesized amino acids, in the absence of a better definition, is used in this paper and generally recommended for use in the corresponding literature.

<A NAME="RM01808SS-2">2</A> Soloshonok VA. Cai C. Hruby VJ. Meervelt L. Tetrahedron 1999, 55: 12045

<A NAME="RM01808SS-3A">3a</A> Fluorine-Containing Amino Acids. Synthesis and Properties Kukhar’ VP. Soloshonok VA. Wiley; Chichester: 1994.

<A NAME="RM01808SS-3B">3b</A> O’Hagan D. Schaffrath C. Cobb S. Hamilton JTG. Murphy CD. Nature 2002, 416: 279

<A NAME="RM01808SS-4A">4a</A> Wang L. Brock A. Herberich B. Schultz PG. Science 2001, 292: 498

<A NAME="RM01808SS-4B">4b</A> Deiters A. Cropp AT. Mukherji M. Chin JW. Anderson CJ. Schultz PG. J. Am. Chem. Soc. 2003, 125: 11782

<A NAME="RM01808SS-5">5</A> Hruby VJ. Lu G. Haskell-Luevano C. Shenderovich MD. Biopolymers (Peptide Science) 1997, 43: 219 ; and references cited therein

<A NAME="RM01808SS-6">6</A> Gibson SE. Guillo N. Tozer MJ. Tetrahedron 1999, 55: 585 ; and references cited therein

For monographs, see:

<A NAME="RM01808SS-7A">7a</A> Molecular Conformation and Biological Interactions Balaram P. Ramaseshan S. Indian Academy of Science; Bangalore: 1991.

<A NAME="RM01808SS-7B">7b</A> Advances in Amino Acid Mimetics and Peptidomimetics Abell A. JAI Press Inc.; Greenwich: 1999. p.191-220

<A NAME="RM01808SS-8">8</A> Special issue on Protein Design, Guest Editor DeGrado WF. Chem. Rev. 2001, 101: 3025-3032

<A NAME="RM01808SS-9">9</A> For a recent collection of papers, see the Special Issue: Asymmetric Synthesis of Novel Sterically Constrained Amino Acids, Tetrahedron Symposia-in-Print # 88; Guest Editors Hruby VJ. Soloshonok VA. Tetrahedron 2001, 57: 6329-6650

For general reviews on asymmetric synthesis of α-amino acids, see:

<A NAME="RM01808SS-10A">10a</A> Cativiela C. Diaz-de-Villegas MD. Tetrahedron: Asymmetry 1998, 9: 3517

<A NAME="RM01808SS-10B">10b</A> Cativiela C. Diaz-de-Villegas MD. Tetrahedron: Asymmetry 2000, 11: 654

<A NAME="RM01808SS-10C">10c</A> Duthaler RO. Tetrahedron 1994, 50: 1539

<A NAME="RM01808SS-10D">10d</A> Nájera C. Sansano JM. Chem. Rev. 2007, 107: 4584

<A NAME="RM01808SS-11">11</A> Gomez-Catalan J. Perez JJ. Jimenez AI. Cativiela C. J. Pept. Sci. 1999, 5: 251

<A NAME="RM01808SS-12A">12a</A> Masumoto S. Usuda H. Suzuki M. Kanai M. Shibasaki M. J. Am. Chem. Soc. 2003, 125: 5634

<A NAME="RM01808SS-12B">12b</A> Kato N. Suzuki M. Kanai M. Shibasaki M. Tetrahedron Lett. 2004, 45: 3147

<A NAME="RM01808SS-12C">12c</A> Kato N. Suzuki M. Kanai M. Shibasaki M. Tetrahedron Lett. 2004, 45: 3153

<A NAME="RM01808SS-12D">12d</A> Fujimori I. Mita T. Maki K. Shiro M. Sato A. Furusho S. Kanai M. Shibasaki M. J. Am. Chem. Soc. 2006, 128: 16438

<A NAME="RM01808SS-12E">12e</A> Fujimori I. Mita T. Maki K. Shiro M. Sato A. Furusho S. Kanai M. Shibasaki M. Tetrahedron 2007, 63: 5820

<A NAME="RM01808SS-13A">13a</A> Ooi T. Uematsu Y. Maruoka K. J. Am. Chem. Soc. 2006, 128: 2548

<A NAME="RM01808SS-13B">13b</A> Ooi T. Uematsu Y. Fujimoto J. Fukumoto K. Maruoka K. Tetrahedron Lett. 2007, 48: 1337

<A NAME="RM01808SS-13C">13c</A> Ooi T. Kato D. Inamura K. Ohmatsu K. Maruoka K. ,

<A NAME="RM01808SS-14A">14a</A> Ohfune Y. Shinada T. Eur. J. Org. Chem. 2005, 5127

<A NAME="RM01808SS-14B">14b</A> Ohfune Y. Shinada T. Bull. Chem. Soc. Jpn. 2003, 76: 1115

<A NAME="RM01808SS-14C">14c</A> Namba K. Shinada T. Teramoto T. Ohfune Y. J. Am. Chem. Soc. 2000, 122: 10708

<A NAME="RM01808SS-14D">14d</A> Moon S.-H. Ohfune Y. J. Am. Chem. Soc. 1994, 116: 7405

<A NAME="RM01808SS-15A">15a</A> Davis FA. Liang C.-H. Liu H. J. Org. Chem. 1997, 62: 3796

<A NAME="RM01808SS-15B">15b</A> Davis FA. Liu H. Zhou P. Fang T. Reddy GV. Zhang Y. J. Org. Chem. 1999, 64: 7559

<A NAME="RM01808SS-16A">16a</A> Fitzi R. Seebach D. Tetrahedron 1988, 44: 5277

<A NAME="RM01808SS-16B">16b</A> Kazmierski WM. Urbanczyk-Lipkowska Z. Hruby VJ. J. Org. Chem. 1994, 59: 1789

<A NAME="RM01808SS-17">17</A> Soloshonok VA. Tang X. Hruby VJ. Meervelt LV. Org. Lett. 2001, 3: 341

For selected recent reviews, see:

<A NAME="RM01808SS-18A">18a</A> Calmes M. Daunis J. Amino Acids 1999, 16: 215

<A NAME="RM01808SS-18B">18b</A> Bouifraden S. Drouot C. El Hadrami M. Guenoun F. Lecointe L. Mai N. Paris M. Pothion C. Sadoune M. Sauvagnat B. Amblard M. Aubagnac JL. Calmes M. Chevallet P. Daunis J. Enjal-bal C. Fehrentz JA. Lamaty F. Lavergne JP. Lazaro R. Rolland V. Roumestant ML. Viallefont P. Vidal Y. Martinez J. Amino Acids 1999, 16: 345

<A NAME="RM01808SS-18C">18c</A> Sutherland A. Willis CL. Nat. Prod. Rep. 2000, 17: 621

<A NAME="RM01808SS-18D">18d</A> Beller M. Eckert M. Angew. Chem. Int. Ed. 2000, 39: 1010

<A NAME="RM01808SS-18E">18e</A> Kawabata T. Fuji K. Synth. Org. Chem. Jpn. 2000, 58: 1095

<A NAME="RM01808SS-18F">18f</A> Kazmaier U. Maier S. Zumpe FL. Synlett 2000, 1523

<A NAME="RM01808SS-18G">18g</A> Yao SL. Saaby S. Hazell RG. Jorgensen KA. Chem. Eur. J. 2000, 6: 2435

<A NAME="RM01808SS-18H">18h</A> Abellan T. Chinchilla R. Galindo N. Guillena G. Najera C. Sansano JM. Eur. J. Org. Chem. 2000, 2689

<A NAME="RM01808SS-18I">18i</A> Rutjes FPJT. Wolf LB. Schoemaker HE. J. Chem. Soc., Perkin Trans. 1 2000, 4197

<A NAME="RM01808SS-18J">18j</A> Shioiri T. Hamada Y. Synlett 2001, 184

<A NAME="RM01808SS-18K">18k</A> Williams RM. Synthesis of Optically Active α-Amino Acids Pergamon Press; Oxford: 1989.

<A NAME="RM01808SS-19A">19a</A> Belokon YN. Janssen Chim. Acta 1992, 10 (2): 4

<A NAME="RM01808SS-19B">19b</A> Belokon YN. Pure Appl. Chem. 1992, 64: 1917

<A NAME="RM01808SS-20">20</A> Ueki H. Ellis TK. Martin CH. Bolene SB. Boettiger TU. Soloshonok VA. J. Org. Chem. 2003, 68: 7104

<A NAME="RM01808SS-21A">21a</A> Andronova IG. Maleev VI. Ragulin VV. Il’in MM. Tsvetkov EN. Belokon’ YuN. Zh. Obshch. Khim. 1996, 66: 1096

<A NAME="RM01808SS-21B">21b</A> Tararov VI. Savel’eva TF. Kuznetsov NYu. Ikonnikov NS. Orlova SA. Belokon’ YuN. North M. Tetrahedron: Asymmetry 1997, 8: 79

<A NAME="RM01808SS-21C">21c</A> Sagiyan AS. Dzhamgaryan SM. Grigoryan GL. Kagramanyan SR. Ovsepyan GTs. Grigoryan SK. Belokon’ YuN. Khimich. Zh. Armenii 1996, 49: 75

<A NAME="RM01808SS-21D">21d</A> Sagiyan AS. Grigoryan SK. Dzhamgaryan SM. Grigoryan GL. Belokon’ YuN. Khimich. Zh. Armenii 1996, 49: 142

<A NAME="RM01808SS-21E">21e</A> Belokon’ YN. Kochetkov KA. Ikonnikov NS. Strelkova TV. Harutyunyan SR. Saghiyan AS. Tetrahedron: Asymmetry 2001, 12: 481

<A NAME="RM01808SS-21F">21f</A> Larionov OV. Savel’eva TF. Kochetkov KA. Ikonnokov NS. Kozhushkov SI. Yufit DS. Howard JAK. Khrustalev VN. Belokon YN. de Meijere A. Eur. J. Org. Chem. 2003, 869

<A NAME="RM01808SS-21G">21g</A> Belokon YN. Kochetkov KA. Borkin DA. Mendeleev Commun. 2003, 132

<A NAME="RM01808SS-21H">21h</A> Belokon YN. Maleev VI. Savel’eva TF. Moskalenko MA. Pripadchev DA. Khrustalev VN. Vorontsov EV. Sagiyan AS. Babayan EP. Russ. Chem. Bull. 2005, 54: 981

<A NAME="RM01808SS-22A">22a</A> Soloshonok VA. Belokon YN. Kukhar VP. Chernoglazova NI. Saporovskaya MB. Bakhmutov VI. Kolycheva MT. Belikov VM. Izv. Akad. Nauk SSSR, Ser. Khim. 1990, 1630

<A NAME="RM01808SS-22B">22b</A> Soloshonok VA. Kukhar VP. Galushko SV. Kolycheva MT. Rozhenko AB. Belokon YN. Izv. Akad. Nauk SSSR, Ser. Khim. 1991, 1166

<A NAME="RM01808SS-22C">22c</A> Soloshonok VA. Kukhar VP. Batsanov AS. Galakhov MA. Belokon YN. Struchkov YT. Izv. Akad. Nauk SSSR, Ser. Khim. 1991, 1548

<A NAME="RM01808SS-22D">22d</A> Soloshonok VA. Kukhar VP. Galushko SV. Rozhenko AB. Kuzmina NA. Kolycheva MT. Belokon YN. Izv. Akad. Nauk SSSR, Ser. Khim. 1991, 1906

<A NAME="RM01808SS-22E">22e</A> Soloshonok VA. Svistunova NY. Kukhar VP. Gudima AO. Kuzmina NA. Belokon YN. Izv. Akad. Nauk SSSR, Ser. Khim. 1992, 117

<A NAME="RM01808SS-22F">22f</A> Soloshonok V. A., Svistunova N. Y., Kukhar V. P., Solodenko V. A., Kuzmina N. A., Rozhenko A. B., Galushko S. V., Shishkina I. P., Gudima A. O., Belokon Y. N.; Izv. Akad. Nauk SSSR, Ser. Khim.; 1992, 397

<A NAME="RM01808SS-22G">22g</A> Soloshonok VA. Svistunova NY. Kukhar VP. Kuzmina NA. Belokon YN. Izv. Akad. Nauk SSSR, Ser. Khim. 1992, 687

<A NAME="RM01808SS-22H">22h</A> Soloshonok VA. Belokon YN. Kuzmina NA. Maleev VI. Svistunova NY. Solodenko VA. Kukhar VP. J. Chem. Soc., Perkin Trans. 1 1992, 1525

<A NAME="RM01808SS-22I">22i</A> Kukhar VP. Belokon YN. Svistunova NY. Soloshonok VA. Rozhenko AB. Kuzmina NA. Synthesis 1993, 117

<A NAME="RM01808SS-22J">22j</A> Soloshonok VA. Svistunova NY. Kukhar VP. Kuzmina NA. Popov VI. Belokon YN. Izv. Akad. Nauk SSSR, Ser. Khim. 1993, 786

<A NAME="RM01808SS-22K">22k</A> Soloshonok VA. Kukhar VP. Galushko SV. Svistunova NY. Avilov DV. Kuzmina NA. Raevski NI. Struchkov YT. Pisarevsky AP. Belokon YN. J. Chem. Soc., Perkin Trans. 1 1993, 3143

<A NAME="RM01808SS-22L">22l</A> Kukhar VP. Luik AI. Soloshonok VA. Svistunova NY. Skryma RN. Rybalchenko VV. Belokon YN. Kuzmina NA. Khim. Pharm. Zh. 1994, 27: 35

<A NAME="RM01808SS-22M">22m</A> Soloshonok VA. Avilov DV. Kukhar VP. Tararov VI. Saveleva TF. Churkina TD. Ikonnikov NS. Kochetkov KA. Orlova SA. Pysarevsky AP. Struchkov YT. Raevsky NI. Belokon YN. Tetrahedron: Asymmetry 1995, 6: 1741

<A NAME="RM01808SS-22N">22n</A> Soloshonok VA. Gerus II. Yagupolskii YL. Kukhar VP. Zh. Org. Khim. 1987, 23: 2308 ; Chem. Abstr. 1988, 109, 55185

<A NAME="RM01808SS-22O">22o</A> Basyuk VA. Gromovoi TY. Chuiko AA. Soloshonok VA. Kukhar VP. Synthesis 1992, 449

<A NAME="RM01808SS-23A">23a</A> Soloshonok VA. Avilov DV. Kukhar VP. Tetrahedron: Asymmetry 1996, 7: 1547

<A NAME="RM01808SS-23B">23b</A> Soloshonok VA. Avilov DV. Kukhar VP. Tetrahedron 1996, 52: 12433

<A NAME="RM01808SS-23C">23c</A> Soloshonok VA. Avilov DV. Kukhar’ VP. Meervelt LV. Mischenko N. Tetrahedron Lett. 1997, 38: 4671

<A NAME="RM01808SS-23D">23d</A> Soloshonok VA. Avilov DV. Kukhar’ VP. Meervelt LV. Mischenko N. Tetrahedron Lett. 1997, 38: 4903

<A NAME="RM01808SS-23E">23e</A> Soloshonok VA. Cai C. Hruby VJ. Meervelt LV. Mischenko N. Tetrahedron 1999, 55: 12031

<A NAME="RM01808SS-23F">23f</A> Soloshonok VA. Cai C. Hruby VJ. Meervelt LV. Tetrahedron 1999, 55: 12045

<A NAME="RM01808SS-23G">23g</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron: Asymmetry 1999, 10: 4265

<A NAME="RM01808SS-23H">23h</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron Lett. 2000, 41: 135

<A NAME="RM01808SS-23I">23i</A> Soloshonok VA. Cai C. Hruby VJ. Org. Lett. 2000, 2: 747

<A NAME="RM01808SS-23J">23j</A> Qiu W. Soloshonok VA. Cai C. Tang X. Hruby VJ. Tetrahedron 2000, 56: 2577

<A NAME="RM01808SS-23K">23k</A> Soloshonok VA. Cai C. Hruby VJA. Angew. Chem. Int. Ed. 2000, 39: 2172

<A NAME="RM01808SS-23L">23l</A> Tang X. Soloshonok VA. Hruby VJ. Tetrahedron: Asymmetry 2000, 11: 2917

<A NAME="RM01808SS-23M">23m</A> Soloshonok VA. Cai C. Hruby VJ. Meervelt LV. Yamazaki T. J. Org. Chem. 2000, 65: 6688

<A NAME="RM01808SS-23N">23n</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron Lett. 2000, 41: 9645

<A NAME="RM01808SS-23O">23o</A> Cai C. Soloshonok VA. Hruby VJ. J. Org. Chem. 2001, 66: 1339

<A NAME="RM01808SS-23P">23p</A> Soloshonok VA. Tang X. Hruby VJ. Tetrahedron 2001, 57: 6375

<A NAME="RM01808SS-23Q">23q</A> Soloshonok VA. Curr. Org. Chem. 2002, 6: 341

<A NAME="RM01808SS-23R">23r</A> Ellis TK. Hochla VM. Soloshonok VA. J. Org. Chem. 2003, 68: 4973

<A NAME="RM01808SS-23S">23s</A> Taylor SM. Yamada T. Ueki H. Soloshonok VA. Tetrahedron Lett. 2004, 45: 9159

<A NAME="RM01808SS-23T">23t</A> Soloshonok VA. Cai C. Yamada T. Ueki H. Ohfune Y. Hruby VJ. J. Am. Chem. Soc. 2005, 127: 15296

<A NAME="RM01808SS-23U">23u</A> Soloshonok VA. Yamada T. Ueki H. Moore AM. Cook TK. Arbogast KL. Soloshonok AV. Martin CH. Ohfune Y. Tetrahedron 2006, 62: 6412

<A NAME="RM01808SS-23V">23v</A> Soloshonok VA. Ueki H. J. Am. Chem. Soc. 2007, 129: 2426

<A NAME="RM01808SS-24A">24a</A> Fishwick CWG. Sanderson JM. Findlay JBC. Tetrahedron Lett. 1994, 35: 4611

<A NAME="RM01808SS-24B">24b</A> Chen B.-H. Nie J.-Y. Singh M. Pike VW. Kirk KL. J. Fluorine Chem. 1995, 75: 93

<A NAME="RM01808SS-24C">24c</A> Kliukiene R. Maroziene A. Stumbreviciute Z. Karpavicius K. Chemija 1996, 3: 76

<A NAME="RM01808SS-24D">24d</A> Mosevich IK. Kuznetsova OF. Fedorova OS. Korsakov MV. Radiochemistry (Moscow) 1996, 38: 511

<A NAME="RM01808SS-24E">24e</A> Jirman J. Nadvornik M. Sopkova J. Popkov A. Magn. Reson. Chem. 1998, 36: 351

<A NAME="RM01808SS-24F">24f</A> Collet S. Bauchat P. Danion-Bougot R. Danion D. Tetrahedron: Asymmetry 1998, 9: 2121

<A NAME="RM01808SS-24G">24g</A> Popkov A. Jirman J. Nadvornik M. Manorik PA. Collect. Czech. Chem. Commun. 1998, 63: 990

<A NAME="RM01808SS-24H">24h</A> Popkov AN. Nadvornik M. Iirman I. Sopkova Ya. Manorik PA. Fedorenko MA. Russ. J. Gen. Chem. 1998, 68: 1242

<A NAME="RM01808SS-24I">24i</A> Mosevich IK. Kuznetsova OF. Vasil’ev DA. Anichkov AA. Korsakov MV. Radiochemistry (Moscow) 1999, 41: 273

<A NAME="RM01808SS-24J">24j</A> Collet S. Carreaux F. Boucher J.-L. Pethe S. Lepoivre M. Danion-Bougot R. Danion D. J. Chem. Soc., Perkin Trans. 1 2000, 177

<A NAME="RM01808SS-24K">24k</A> Debache A. Collet S. Bauchat P. Danion D. Euzenat L. Hercouet A. Carboni B. Tetrahedron: Asymmetry 2001, 12: 761

<A NAME="RM01808SS-24L">24l</A> Nadvornik M. Popkov A. Green Chem. 2002, 4: 71

<A NAME="RM01808SS-24M">24m</A> Gu X. Tang X. Cowell S. Ying J. Hruby VJ. Tetrahedron Lett. 2002, 43: 6669

<A NAME="RM01808SS-24N">24n</A> Hashimoto M. Hatanaka Y. Sadakane Y. Nabeta K. Bioorg. Med. Chem. Lett. 2002, 12: 2507

<A NAME="RM01808SS-24O">24o</A> Zhang J. Xiong C. Ying J. Wang W. Hruby VJ. Org. Lett. 2003, 5: 3115

<A NAME="RM01808SS-24P">24p</A> Chaykovski MM. Bae LC. Cheng M.-C. Murray JH. Tortolani KE. Zhang R. Seshadri K. Findlay JHBC. Hsieh S.-Y. Kalverda AP. Homans SW. Brown JM. J. Am. Chem. Soc. 2003, 125: 15767

<A NAME="RM01808SS-24Q">24q</A> Gu X. Ndungu JM. Qiu W. Ying J. Carducci MD. Wooden H. Hruby VJ. Tetrahedron 2004, 60: 8233

<A NAME="RM01808SS-24R">24r</A> Hao B. Zhao G. Kang PT. Soares JA. Ferguson TK. Gallucci J. Krzycki JA. Chan MK. Chem. Biol. 2004, 11: 1317

<A NAME="RM01808SS-24S">24s</A> Ouchi H. Kumagai M. Sakurada S. Takahata H. Heterocycles 2004, 64: 505

<A NAME="RM01808SS-24T">24t</A> Ghalit N. Poot AJ. Fuerstner A. Rijkers DTS. Liskamp RMJ. Org. Lett. 2005, 7: 2961

<A NAME="RM01808SS-24U">24u</A> Pessoa JC. Correia I. Galvao A. Gameiro A. Felix V. Fiuza E. Dalton Trans. 2005, 2312

<A NAME="RM01808SS-24V">24v</A> Vadon-Legoff S. Dijols S. Mansuy D. Boucher J.-L. Org. Process Res. Dev. 2005, 9: 677

<A NAME="RM01808SS-24W">24w</A> Popkov A. Cisarova I. Sopkova J. Jirman J. Lycka A. Kochetkov KA. Collect. Czech. Chem. Commun 2005, 70: 1397

<A NAME="RM01808SS-24X">24x</A> Saghiyan AS. Dadayan SA. Petrosyan SG. Manasyan LL. Geolchanyan AV. Djamgaryan SM. Andreasyan SA. Maleev VI. Khrustalev VN. Tetrahedron: Asymmetry 2006, 17: 455

<A NAME="RM01808SS-24Y">24y</A> Saghiyan AS. Geolchanyan AV. Synth. Commun. 2006, 36: 3667

<A NAME="RM01808SS-24Z">24z</A> Langer V. Popkov A. Nadvornik M. Lycka A. Polyhedron 2007, 26: 911

As shown previously (see refs. 21-23), CD and ORD spectra of Ni(II) complexes of this type in neutral solutions exhibit two maxima in the region of metal d-d transition (Cotton effects at 450 and 550 nm). In the ORD spectra, the sign of Cotton effects in this region strictly depends upon a conformation of the polycyclic system of chelate rings. Thus, in the case of complexes containing α-monosub-stituted α-amino acid, the pseudoaxial orientation of the amino acid side chain, corresponding to α-l configuration of α-amino acid, causes a Cotton effect with a positive sign at the 500-700 nm region and negative sign at 400-450 nm. Consequently, a pseudoequatorial orientation of the amino acid side chain brings about opposite signs of the Cotton effects at 400-450 (positive) and at the 500-700 nm (negative) regions. As established in numerous studies, this general trend is not influenced by the structure and nature of the α-amino acid side chain, and the configuration of stereogenic centers within it.

<A NAME="RM01808SS-26">26</A> For the complex containing (2S,3R)-3-phenylglutamic acid, the α-proton appears at δ = 4.14 (J _α _H, _β _H = 3.7 Hz); for the complex containing (2S,3S)-3-phenylglutamic acid, the α-proton is at δ = 4.07 (J _α _H, _β _H = 7.0 Hz); for details, see: Belokon’ YuN. Bulychev AG. Ryzhov MG. Vitt SV. Batsanov AS. Struchkov YuT. Bakhmutov VI. Belikov VM. J. Chem. Soc., Perkin Trans. 1 1986, 1865

<A NAME="RM01808SS-27">27</A> Dharanipragada R. VanHulle K. Bannister A. Bear S. Kennedy L. Hruby VJ. Tetrahedron 1992, 48: 4733

<A NAME="RM01808SS-28A">28a</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron: Asymmetry 1999, 10: 4265

<A NAME="RM01808SS-28B">28b</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron Lett. 2000, 41: 135

<A NAME="RM01808SS-28C">28c</A> Soloshonok VA. Cai C. Hruby VJ. Org. Lett. 2000, 2: 747

<A NAME="RM01808SS-28D">28d</A> Soloshonok VA. Cai C. Hruby VJ. Angew. Chem. Int. Ed. 2000, 39: 2172

<A NAME="RM01808SS-28E">28e</A> Soloshonok VA. Cai C. Hruby VJ. Meervelt LV. Yamazaki T. J. Org. Chem. 2000, 65: 6688

<A NAME="RM01808SS-28F">28f</A> Soloshonok VA. Cai C. Hruby VJ. Tetrahedron Lett. 2000, 41: 9645

<A NAME="RM01808SS-28G">28g</A> Cai C. Soloshonok VA. Hruby VJ. J. Org. Chem. 2001, 66: 1339

<A NAME="RM01808SS-28H">28h</A> Soloshonok VA. Ueki H. Tiwari R. Cai C. Hruby VJ. J. Org. Chem. 2004, 69: 4984

<A NAME="RM01808SS-28I">28i</A> Cai C. Yamada T. Tiwari R. Hruby VJ. Soloshonok VA. Tetrahedron Lett. 2004, 45: 6855

<A NAME="RM01808SS-28J">28j</A> Soloshonok VA. Ueki H. Ellis TK. Tetrahedron Lett. 2005, 46: 941

<A NAME="RM01808SS-28K">28k</A> Soloshonok VA. Ueki H. Ellis TK. Yamada T. Ohfune Y. Tetrahedron Lett. 2005, 46: 1107

<A NAME="RM01808SS-28L">28l</A> Soloshonok VA. Ellis TK. Synlett 2006, 533

<A NAME="RM01808SS-28M">28m</A> Ellis TK. Ueki H. Yamada T. Ohfune Y. Soloshonok VA. J. Org. Chem. 2006, 71: 8572