Pyrimidines. III. 5,6-Dihydropyrimidines<sup>1</sup>

Zee-Cheng, Kwang-Yuen; Robins, Roland K.; Cheng, C. C.

doi:10.1021/jo01065a046

Cited by 40 publications

(14 citation statements)

References 2 publications

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“…For 1 h, 5,6 -dihydro -6,6 -dimethyluracil (prepared according to [38]; a sample recrystallized from EtOH melted at 204" ( [38]: m.p. 202")) (2.89 g, 0.02 mol) was heated in boiling aq.…”

Section: Boc-(ss)-~-mentioning

confidence: 99%

Probing the Helical Secondary Structure of Short‐Chain β‐Peptides

Seebàch¹,

Ciceri

Overhand

et al. 1996

Helvetica Chimica Acta

519

798

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Dedicated to Professor Teruaki Mukaiyuma, a dear friend and revered colleague on the occasion of his 70th birthday(1 3. VIII. 96)Structural prerequisites for the stability of the 3, helix of p-peptides can be defined from inspection of models (Figs. 1 and 2 ) : lateral non-Hi-substituents in 2-and 3-position on the 3-amino-acid residues of the helix are allowed, axial ones are forbidden. To be able to test this prediction, we synthesized a series of hepta- (1) and of the p-heptapeptide H-P-HVal-P-HAla-p-HLeu-(S,S)-~-HAla(a Me)-p-HVal-p-HAla-p-HLeu-OH (22), with a central (2S,3S)-3-amino-2-methylbutanoic-acid residue, confirm the helical structure of such 8-peptides (previously discovered in pyridine solution) (Fig. 3 and Tables 1-5). The CD spectra of helicalp-peptides, the residues of which were prepared by (retentive) Arndt-Eistert homologation of the (S)-or ~-a-amino acids, show a trough at 215 nm. Thus, this characteristic pattern of the CD spectra was taken as an indicator for the presence of a helix in methanol solutions of compounds 1 S 2 2 and 25 (including partially and fully deprotected forms) (Figs. 4 4 ) . The results fully confirm predicted structural effects: incorporation of a single 'wrong' residue ((R)-P-HAla, p-HAib, (R,S)-B-HAla(aMe), or N-Me-P-HAla) in the central positioh of thep-heptapeptide derivatives A (see 17, 18,20, or 21, resp.) causes the CD minimum to disappear. Also, the P-heptadepsipetide 25 (missing H-bond) and the /I-heptapeptide analogs with a single a-amino-acid moiety in the middle (13 and 14) are not helical, according to this analysis. An interesting case is the heptapeptide 15 with the central achiral, unsubstituted 3-aminopropanoicacid moiety: helical conformation appears to depend upon the presence or absence of terminal protection and upon the solvent (MeOH vs. MeOH/H20).

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“…For 1 h, 5,6 -dihydro -6,6 -dimethyluracil (prepared according to [38]; a sample recrystallized from EtOH melted at 204" ( [38]: m.p. 202")) (2.89 g, 0.02 mol) was heated in boiling aq.…”

Section: Boc-(ss)-~-mentioning

confidence: 99%

Probing the Helical Secondary Structure of Short‐Chain β‐Peptides

Seebàch¹,

Ciceri

Overhand

et al. 1996

Helvetica Chimica Acta

519

798

View full text Add to dashboard Cite

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“…4 Hz, H-2 and H-6); 7.81 (2H, d, J ¼ 8. 7 Hz, H-3 and H-5); 7.66 (2H, d, J ¼ 9. 6 Hz, H-2 00 and H-6 00 ); 6.92 (2H, d, J ¼ 9.…”

Section: -[4mentioning

confidence: 99%

“…To this the diazonium solution was added dropwise, keeping the temperature at 5 C and reaction pH at 10 (5 N NaOH was added when necessary). The solution was either neutralized to pH 7 (for compound 7) or stirred continuously at room temperature (for compound 8).…”

Section: -[4mentioning

confidence: 99%

“…5-Amino-1-(4 0 -carboxyphenyl)-1H-pyrazole-4-carbonitrile (1b)It was obtained as an orange solid (yield 94%), recrystallized from ethanolewater (yield 89%), m.p. 275e277 C.1 H NMR (DMSO-d 6 ) d (ppm): 6.88 (2H, br s, NH 2 ); 7.65 (2H, d, J ¼ 8 7. Hz, H-2 0 and H-6 0 ); 7.84 (1H, s, H-3); 8.06 (2H, d, J ¼ 8 7.…”

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confidence: 99%

“…275e277 C.1 H NMR (DMSO-d 6 ) d (ppm): 6.88 (2H, br s, NH 2 ); 7.65 (2H, d, J ¼ 8 7. Hz, H-2 0 and H-6 0 ); 7.84 (1H, s, H-3); 8.06 (2H, d, J ¼ 8 7. Hz, H-3 0 and H-5 0 ); 13.15 (1H, br s, COOH).…”

mentioning

confidence: 99%

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