Substrate analogs

The somewhat analogous substrate, p-methoxy-A-(2-nitroprop-l-enyl)aniline (15), afforded 6-methoxy-3-methylquinoxaline 4-oxide (16) (98% H2SO4 %). ... 

An analogous substrate, dimethyl 10-chloro-7-methyl-6-oxo-l lb-phenyl-5,6,7,1 lb-tetrahydroisoxazolo[2,3-d][l,4]benzodiazepine-l,2-dicarboxylate (566), gave not 567 but 6-chloro-l-methyl-2(l/7)-quinoxalinone (EtOH, reflux, 30 h -40%). ... 

In general there are few reproducible data on binding of reducible substrates to the isolated MoFe proteins. However, the S = EPR signal from the FeMoco centers of Kpl is pH dependent, the g values changing with a pKa of 8.7 (50). Of course, the proton is a substrate of nitrogenase however, there is no direct evidence for the proton associated with the pKa being bound directly to FeMoco. Nevertheless, this pKa can be perturbed by addition of the analog substrate acety-... 

The signiflcance of toxic metabolites is important in diverse metabolic situations (a) when a pathway results in the synthesis of a toxic or inhibitory metabolite, and (b) when pathways for the metabolism of two (or more) analogous substrates supplied simultaneously are incompatible due to the production of a toxic metabolite by one of the substrates. A number of examples are provided to illustrate these possibilities that have achieved considerable attention in the context of the biodegradation of chlorinated aromatic compounds (further discussion is given in Chapter 9, Part 1) ... 

There may be several reasons why an analog substrate cannot be metabolized by an organism. This is well illustrated by 4-ethylbenzoate that could not be used by strains that degraded 3- and 4-methylbenzoate (Ramos et al. 1987). There were two reasons ... 

Some enzymes have a low snbstrate specificity, and are able to accept analog substrates with the formation of colored metabolites. This may be used to detect enzymatic activity toward the desired substrates when a large number of colonies have to be examined. Examples inclnde the following ... 

Effectiveness of analog substrates and metabolites in promoting degradation... 

Analogous substrates were used for an intramolecular Heck reaction to obtain indolizidinone derivatives (Scheme 33) <2000SL319, 2002S87>. 

To improve the scope of the Lossen rearrangement, other structural analogous substrates to hydroxamic acids have been tested. Af-Phosphinoylhydroxylamines are the phosphorus analogues of hydroxamic acids and, when suitably activated, they undergo a Lossen-Uke rearrangement in the presence of base. 

In this work we extend our study to the hydrogenation and isomerization of a series of a,p-unsaturated alcohols, such as 2-propen-l-ol (A2), (E -2-buten-l-ol (EB2), (" -2-penten-l-ol (ZP2), (E -2-penten-l-ol (EP2), (" -2-hexen-l-ol (ZH2), (E -2-hexen-l-ol (EH2), carried out in the presence of RhCl(PPh3)3, with and without triethylamine (NEts), at 303 K, using ethanol as solvent. The major targets of our research are to investigate the influence of the unsaturated alcohol structure on the product distribution and to verify the possibility of extending the results, previously obtained with (" -2-butene-1,4-diol, to other analogous substrates. 

Pasti, C. Gallois-Montbrun, S. Munier-Lehmann, H. Veron, M. Gilles, A.M. Deville-Bonne, D. Reaction of human UMP-CMP kinase with natural and analog substrates. Eur. J. Biochem., 270, 1784-1790 (2003)... 

Figure 4 Analogous substrates of hydrolytic Fe/S enzymes, (a) Citrate (R = acetyl), isopropylmalate (R = propyl), malate (R = H) (b) serine (c) dihydroxyvalerate (R = methyl), dihydroxymethylvalerate (R = ethyl).

Oxo-l,4-dihydro-l,5-naphthyridine-3-carboxylic acid (21, R = H) gave l-ethyl-4-oxo-l,4-dihydro-l,5-naphthyridine-3-carboxylic acid (21, R = Et) (EtI, KOH, H20, EtOH, reflux, 3.5 h 50%) 911 the analogous substrate, ethyl 7-methyl-4-oxo-l,4-dihydro-l,5-naphthyridine-3-carboxylate (22, R = H), gave ethyl 1 -ethyl-7-methyl-4-oxo-1,4-dihydro-1,5-naphthyridine-3-carboxy-late (22, R = Et) (substrate, NaH, Me2NCHO, 20°C, 20 min then Etl, 50°C, 5 h, then 20°C, 12 h 50%).1398... 

Ethyl 3-(2-ethoxycarbonylethyl)-4-phenlimino-l-piperidinecarboxylate (20) underwent reductive cyclization to ethyl 2-oxo-l-phenyl-l,2,3,4,5,6,7,8-octa-hydro-l,6-naphthyridine-l-carboxylate (21) (NaBH4, dioxane, 20°C, 12h 27%) or its decahydro analog (substrate, THF, HC1 gas [, NaBH3CN/MeOH [ slowly, 20°C, 3.5 h 22%).1104... 

The analogous substrate, ethyl 2-(iV-benzyl-iV-ethoxycarbonylmethylamino-methyl)-3-pyridinecarboxylate (15), gave only a nucleus-reduced product, ethyl 7-benzyl-5-hydroxy-7,8-dihydro-l,7-naphthyridine-6-carboxylate (16)... 

Ethyl 6-amino-l-ethyl- (17, R = Et, X = NH2) gave ethyl 6-chloro-l-ethyl-7-methyl-4-oxo-l,4-dihydro-l,8-naphthyridine-3-carboxylate (17, R = Et, X = C1) (HN02, 0°C CuCl, 65°C 64%) 387 an analogous substrate,(17, R = H, X = NH2), likewise gave l-ethyl-6-fluoro-7-methyl-4-oxo-l,4-dihy-dro-l,8-naphthyridine-3-carboxylic acid (17, R = H, X = F) (NaNQ2, HBF4,... 

The previous assignment of stereochemistry to isolongifolene epoxide (149)66 has been confirmed by epoxidation studies with analogous substrates.67 It has also been concluded that the factors controlling the stereochemistry of epoxidation are the bicyclohepty moiety and the C-2/3 methyl group. 

Again, only one example of this synthesis has been reported. Like the analogous substrate (140), isobutyl 1,1 -dimethyl-5,8-dioxo-1,5,6,7,8,8a-hexahydro-3//-thia-/oIo13,4-a pyrazine-3-carboxyIic acid (142) underwent hssion and desulfurization (on stirring with ethanolic Raney nickel at 20°C for 12 h) to afford an hydropy-razine, this time l-isobutoxycarbonylmethyl-6-isopropyl-3,6-dihydro-2,5(l//, 4H)-pyrazinedione (143) in 89% yield.1255... 

It is worth noting here that different types of R-XH substrates (Fig. 12), due to their nucleophilicity, can easily react with formaldehyde to give methylol derivatives (12), which behave, in turn, as X-methylating agents toward other analogous substrates R—YH. 

Same results reported with analogous substrates... 

The silanized surfaces were characterized by DRIFT ( ffiise reflectance infrared jfourier fransform) spectroscopy [1, 2], Fig. 2-4 show the DRIFT-spectra of untreated silica gel and the analogous substrate after application of l-octenyl-8-dimethylethoxysilane or of the copolymer. 

Deuteration experiments showed that the p-H atom in the product stems from borohydride whereas the a-H atom is introduced by proton transfer from ethanol. Formation of the a-(C-H) bond is nonstereoselective accordingly, the reduction of analogous substrates with an a- instead of a p-disubstituted double bond leads to racemic products (a mechanistic model rationalizing the stereoselectivity of (semicorrinato)cobalt catalysts is available ). 

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