Regiochemical assignment of methylated purines and pyrimidines by selective INEPT

Osterman, Rebecca; McKittrick, Brian A.; Chan, Tze-Ming

doi:10.1016/s0040-4039(00)61219-4

Cited by 16 publications

(11 citation statements)

References 17 publications

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“…The 13 C-NMR and FABMS (MH + , m/z 372) of pallidin (1) supported the molecular formula C 20 H 25 N 3 O 4 (mol wt 371). The pattern of 1 H-NMR signals in the aromatic proton region indicated an indole moiety, and the four signals at δ 7.34, 7.41, 7.63, and 8.86 ppm were attributed to the four neighboring aromatic protons.…”

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confidence: 72%

“…The interpretation of the 1 H-1 H COSY and 1 H- 13 C COSY NMR spectra established the presence of the following three subunits: -HCdCHCHdCH-, -CH 2 -CH 2 CH 2 CH(N)-, and -CH(N)CH(CH 3 )CH 2 (CH 3 ). The connectivities of these subunits were deduced by analyzing the cross-peaks observed in the HMBC spectrum and by comparing the NMR data with those of the known compound austamide.…”

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confidence: 90%

“…The 1 H-and 13 C-NMR chemical shifts and the IR and mass spectrum of compound 2 revealed that it is a cyclodipeptide. Comparison of its spectral data with those reported in the literature, 10 identified compound 2 as cyclo(L-pro-L-leu).…”

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confidence: 99%

“…12 The mp and UV, 1 H-and 13 C-NMR, and mass spectral data of compound 3 were consistent with those of 1,3dimethylxanthine. 13 Experimental Section General Experimental Procedures. Mps were determined on a X 4 apparatus and are uncorrected.…”

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A New N-Carboxyindole Alkaloid from the Marine Sponge Rhaphisia pallida

Su¹,

Zhong²,

Zeng³

et al. 1996

J. Nat. Prod.

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A new indole alkaloid pallidin (1), together with the two known compounds, cyclo(L-pro-L-leu) and 1,3-dimethylxanthine, were isolated from the sponge Rhaphisia pallida. The structures of these metabolites were defined by spectroscopic methods.Substituted diketopiperazine derivatives of several naturally occurring indole alkaloids have been isolated and have exhibited interesting biological activities. 1 For example, barettin, isolated from the marine sponge Geodia baretti, 2 showed inhibiting activity on electrically induced contractions of an isolated Guinea pig ileum, and austamide was one of the toxic principles of moldy maize meal. 3 In a study of the sponge Rhaphisia pallida Ridley (Halichondriidae), we have isolated the new alkaloid pallidin (1), a member of the rare structural class of N-carboxyindole alkaloids. Indole-3-carboxylic acid derivatives have been known from red algae 4,5 and brown algae. 6 So far, there is no example of a naturally occurring N-carboxyindole alkaloid. However, L-carboxyindole itself and some derivatives have been prepared. 7,8 Pallidin is the first isolation of an N-carboxyindole alkaloid from a natural source. Two known compounds, cyclo(L-pro-L-leu) and 1,3-dimethylxanthine, were also obtained from this species.The ethanol extract of R. pallida yielded pallidin (1), cyclo(L-pro-L-leu), and 1,3-dimethylxanthine by vacuum and flash chromatography.The 13 C-NMR and FABMS (MH + , m/z 372) of pallidin (1) supported the molecular formula C 20 H 25 N 3 O 4 (mol wt 371). The pattern of 1 H-NMR signals in the aromatic proton region indicated an indole moiety, and the four signals at δ 7.34, 7.41, 7.63, and 8.86 ppm were attributed to the four neighboring aromatic protons. The 13 C-NMR signal at 166.2 ppm and an IR absorption at 1700 cm -1 established the presence of a COOH group. A typical N-carboxyindole UV absorption strongly supported this determination. 9 The 13 C NMR signal at 131.2 (d) ppm was assigned to C-2 of indole; thus, a part of the structure of 1 must be an N-carboxyindole with a substituent at C-3.The mass spectrum of 1 (Figure 1) gave two important fragments A and B at m/z 161 and m/z 211, respectively, which obviously originated via cleavage of the C 3 -C 9 bond. Fragment A at m/z 161 represents the N-carboxyindole moiety. It lost OH or COOH to display an [A -OH] ion at m/z 144 and an [A -COOH] ion at m/z 116, respectively. This confirmed that the carboxyl group must be located at the N-1 position. In addition, the position of the carboxyl group was unambiguously confirmed by the HMBC spectrum ( Figure 2).The remaining part of the structure was a diketopiperazine system. IR data for 1 showed NH bands at 3393 and 3310 cm -1 and amide carbonyl bands near 1690 and 1644 cm -1 (amide I), which together with the absence of an amide II band clearly suggested the existence of a diketopiperazine system. 2,3 The 1 H-NMR spectrum showed an exchangeable signal at δ 8.37 ppm which was assigned to two NH protons.The interpretation of the 1 H-1 H COSY and 1 H-13 C COSY NMR spectra esta...

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confidence: 72%

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confidence: 90%

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confidence: 99%

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confidence: 99%

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A New N-Carboxyindole Alkaloid from the Marine Sponge Rhaphisia pallida

Su¹,

Zhong²,

Zeng³

et al. 1996

J. Nat. Prod.

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“…The N7 and N9 regioisomers of simple methylated purines have been distinguished by selective INEPT spectra where the N-methyl protons were irradiated and either the C4 or C5 carbon resonance was enhanced. 26 For the R-nucleosides and other unnatural nucleoside analogues, we relied on long-range 1 H-13 C heteronuclear correlation spectroscopy (HMBC) to unambiguously assign the structures. 27 We were able to correlate threebond coupling from the anomeric proton (H1′) to key carbon resonances of the base ( Figure 5).…”

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Stereocontrolled Syntheses of Deoxyribonucleosides via Photoinduced Electron-Transfer Deoxygenation of Benzoyl-Protected Ribo- and Arabinonucleosides

et al. 2000

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The stereocontrolled, de novo syntheses of beta-2'-deoxy-, alpha-2'-deoxy-, beta-3'-deoxy-, and beta-2', 3'-dideoxyribonucleosides are described. Strategically protected ribose, arabinose, and xylose glycosylation precursors were synthesized bearing C2-esters capable of directing Vorbrüggen glycosylation. The key step is the regioselective deoxygenation of the desired hydroxyl group as either the benzoyl- or 3-(trifluoromethyl)benzoyl derivative. This deoxygenation is accomplished via a photoinduced electron-transfer (PET) mechanism using carbazole derivatives as the photosensitizer. The syntheses of the desired deoxynucleoside generally proceed in three steps from a common, readily available precursor.

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The Spectra of Purines ( H 507)

1996

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Regiochemical assignment of methylated purines and pyrimidines by selective INEPT

Cited by 16 publications

References 17 publications

A New N-Carboxyindole Alkaloid from the Marine Sponge Rhaphisia pallida

A New N-Carboxyindole Alkaloid from the Marine Sponge Rhaphisia pallida

Stereocontrolled Syntheses of Deoxyribonucleosides via Photoinduced Electron-Transfer Deoxygenation of Benzoyl-Protected Ribo- and Arabinonucleosides

The Spectra of Purines ( H 507)

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