Is the strong actinomycin D binding of d(5'CGTCGACG3') the consequence of end-stacking?

It has been reported that ACTD binds strongly and cooperatively to a non-GC containing self-complementary octamer d(CGTCGACG) with a 2:1 drug to duplex ratio (Synder et al., 1989). If one views the classic intercalative preference of ACTD for the 5'GpC3' sequence to be the drug favoring the 3'-side of dG, the possibility exists that the drug molecules may in fact stack on the G.C base pairs at both ends of this oligomeric duplex. To investigate this possibility, d(CGTCGACG) and several related oligomers resulting from replacing the terminal base(s) or appending with dT and/or dA are used in a comparative study employing equilibrium titration, thermal denaturation, kinetic, and various spectral measurements. Absorbance titrations at 20 degrees C confirm the strong and highly cooperative nature of ACTD binding to this octamer. The stoichiometric association constants for the binding of the first and second drugs were found to be 1 x 10(5) and 3.2 x 10(7) M-1, respectively. The base replacements of dG and dC at the respective ends resulted in a much weaker ACTD binding affinity, the loss of binding cooperativity, and much faster association and dissociation kinetics. These are consistent with the inability of the drug to stack on the 3'-side of dG due to base replacements. Appending the end(s) with dA and/or dT resulted in some diminution of binding affinity and cooperativity, appearance of slower association kinetic components, and unusually strong 7-amino-ACTD fluorescence enhancement for oligomers with dA or dT attached to dG at the 3'-terminal. To further support our postulate, studies were also made with d(CGACGTCG), which is related to the parent octamer by inverting the A.T pairs. It was found that, despite the altered internal sequence, this oligomer exhibits cooperative ACTD binding and kinetic characteristics very similar to those of the parent octamer, consistent with its ability to end-stack on the 3'-side of dG.

Acid-facilitated supramolecular assembly of G-quadruplexes in d(CGG)4

Molar [K+] induces aggregate formation in d(CGG)4, as evidenced by absorbance, circular dichroic (CD), and gel measurements. The kinetics of this transformation are extremely slow at pH 8 but are found to be greatly facilitated in acidic conditions. Kinetic profiles via absorbance or CD monitoring at single wavelength resemble those of autocatalytic reacting systems with characteristic induction periods. More than 0.8 M KCl is needed to observe the onset of aggregation at 20 degrees C and pH 5.4 within the time span of 1 day. Time-dependent CD spectral characteristics indicate the formation of parallel G-tetraplexes prior to the onset of aggregation. Despite the evidence of K(+)-induced parallel G-quadruplex and higher molecular weight complex formation, both d(TGG)4 and d(CGG)4T fail to exhibit the observed phenomenon, thus strongly implicating the crucial roles played by the terminal G and base protonation of cytosines. A plausible mechanism for the formation of a novel self-assembled structure is speculated. Aided by the C+.C base pair formation, parallel quadruplexes are initially formed and subsequently converted to quadruplexes with contiguous G-tetrads and looped-out cytosines due to high [K+]. These quadruplexes then vertically stack as well as horizontally expand via interquadruplex C+.C base pairing to result in dendrimer-type self-assembled super structures.

N,N-dialkoxycarbonylamino acids from the sodium hydride-mediated reaction of alkyl chloroformates with mixed anhydrides of N-alkoxycarbonylamino acids

Reaction of mixed anhydride R1OCO-NHCHR2-CO-O-COOR3 for R1 = benzyl and tert-butyl and R3 = methyl, ethyl, benzyl and allyl with sodium hydride and R3OCOCl followed by acid hydrolysis gives modest yields of R1OCO-N(R3OCO)CHR2-COOH. The products are contaminated by parent acid R1OCO-NHCHR2-COOH that is not readily removed. About 75% of the acylation originates from intramolecular transfer of the alkyl carbonate moiety; the remainder comes from acylation by the alkyl chloroformate.

Fulminant amebiasis: a clinical evaluation

Two patients with fulminant amebic colitis with colon perforation and concomitant liver abscess were collected over the last 5 years. One patient underwent emergency laparotomy to treat amebic cecal perforation. Diverted ileostomy saved his life. The ileostomy was successfully reversed 6 months later. The other patient underwent 4 laparotomies with more invasive procedures in less than 1 month due to sequential complications of amebiasis. Colon resection with enterostomy miraculously allowed him to survive. In comparison with the latter, who underwent more aggressive surgery and experienced more catastrophic complications, the former with conservative surgery had a smoother clinical result. Thus, conservative operation for colon perforation due to amebiasis is recommended. Besides, thanks to the alertness of doctors, the favorable age of the patients, the advent of new antiamebic and antimicrobial agents, excellent hyperalimentation, the great improvement in medical facilities and postoperative care, the two critical patients eventually survived after several operations, and had a better outcome as compared with the high mortality rate of 87.5% in our hospital 2 decades earlier.

Amino-acid conjugates of the hapten 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone. Synthesis and confirmation of structure

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone (PhOx = CHOEt) was reacted with methylamine, and 2-phenyloxazole-4-carboxylic acid was coupled with methylamine. The spectroscopic properties of the two products were compared in order to confirm that aminolysis of PhOx = CHOEt occurs by displacement of the ethoxy group to give 2-phenyl-4-(substituted-methylene)-5(4H)-oxazolones and not by attack at the oxazolone-carbonyl followed by rearrangement to give 2-phenyloxazole-4-carboxamides. Ten crystalline conjugates were prepared and characterized by reacting PhOx = CHOEt with an excess of unprotected di- and trifunctional amino acid anions followed by purification by washing them with hydrochloric acid.

The craniofacial morphologic structures of the adult with Class III malocclusion

The morphologic study of adults with true Class III malocclusion has seldom been reported. Tracings of lateral cephalograms of 51 Taiwanese adults with true Class III malocclusion were subjected to quadrilateral analysis. Means and standard deviations, t test, correlation analysis, and regressive analysis were used to compare the differences between this group and a reference population of adults with normal occlusion. The results indicated that the maxillary base is shorter and in a more retrusive position in adults with Class III malocclusion. Furthermore, the mandible is in a more protrusive position. The pattern of growth in the Class III malocclusion was found to be horizontal, that is hypodivergent. In diagnosis of the abnormality, the rule of the quadrilateral can provide assistance. That is, the maxillary base length, mandibular base length, anterior lower facial height, and posterior lower facial height can be used to evaluate the abnormality. In postural relationships the sagittal angle, vertical sagittal ratio, and horizontal sagittal ratio can be used as a reference.

[Clinical and experimental study on Ligusticum wallichii mixture in preventing and treating bronchial asthma]

To investigate the significance of Ligusticum wallichii Mixture (LWM) and its possible therapeutical mechanism in bronchial asthma, clinical and experimental studies were carried out.

RESULTS

LWM inhibited bronchospasm induced by histamine and acetylcholine in guinea pigs; the plasma level of TXB2 was decreased remarkably and the incubation period from antigen inhalation to asthma attack could be delayed by LWM; the incidence of asthma and its mortality were reduced in guinea pigs, compared with control, P < 0.01. In addition, the prolonged period of induced asthma attack was negatively correlated to the plasma level of TXB2 in guinea pigs (P < 0.01). It was observed that the plasma level of TXB2 was decreased, the forced expiratory volume in 1 sec (FEV1%) was elevated significantly in asthmatic patients after they were treated by LWM. Moreover, the total effective rate was significantly better than that in the control (92% : 62%). It indicated that: (1) The effects of airway allergic inflammation (AAI) might be the important pathological basis for the bronchial asthma, (2) TXA2 might be an important inflammatory mediator in asthma which could be taken as an useful biochemical parameter for evaluating clinical effects, (3) LWM could relax tracheal smooth muscle, improve pulmonary function, inhibit the synthesis and release of TXA2 with no side effects.

2,4-Dimethyl-5(4H)-oxazolone as reagent for activation and coupling of N-substituted aspartic acid

Reaction of the title oxazolone with N-benzyloxycarbonyl-L-aspartic acid in dichloromethane followed by addition of phenylalanine methyl ester.HCl and N-methylmorpholine gave a 90% yield of a mixture of alpha- and beta-isomers of Z-aspartylphenylalanine methyl esters in a 7:3 ratio. Reaction of the oxazolone with N-acetyl-L-aspartic acid anhydride gave a 75% yield of crystalline N-acetyl-L-aspartic acid anhydride. tert-Butoxycarbonylaspartic and Z-glutamic acids also underwent activation to give the anhydrides.

N-9-fluorenylmethoxycarbonylpyroglutamate. Preparation of the acid, chloride and succinimidyl ester

Fmoc-glutamic acid is converted by thionyl chloride into the dichloride, which spontaneously cyclizes to Fmoc-pyroglutamyl chloride. The latter is stable to water. Pure Fmoc-pyroglutamyl chloride is obtained by washing the reaction mixture with water, which destroys uncyclized dichloride by converting it into the 2-alkoxy-5(4H)-oxazolone that is readily hydrolyzed. Fmoc-pyroglutamic acid and succinimidyl ester are obtained from the chloride by acid hydrolysis and reaction with N-hydroxysuccinimide, respectively.

Oligonucleotide studies of sequence-specific binding of chromomycin A3 to DNA

Systematic kinetic, equilibrium binding, melting, and electrophoretic studies were carried out with oligonucleotides to determine the sequence specificities of chromomycin A3 (CHR) binding to DNA at the self-complementary tetranucleotide level. Decamers of the forms d(GTA-XGCY-TAC) and d(GTA-XCGY-TAC), with X, Y = A, G, C, or T, were used for this purpose. Results indicate that the binding preferences for CHR are in the order -GGCC- > -CGCG- > -GCGC-, -CCGG- > -AGCT- > -ACGT-, -TGCA- > -TCGA-. Detergent-induced drug dissociation studies revealed that CHR dissociates very slowly from both -GGCC- and -CGCG- sequences, with the former being measurably slower than the latter which in turn is at least an order of magnitude slower than the rest of the sequences. Thermal denaturation measurements indicate that the binding of CHR stabilizes the DNA duplex, with -GGCC- and -CGCG- exhibiting the largest effects. Results of gel electrophoretic retardation experiments support our general findings on the relative binding order. Our experimental results support earlier NMR findings by other researchers implicating the preference of aureolic acid drugs at the 5'GC3' step and further reveal significant modulations by the adjacent base pairs. Attempts were made to rationalize our results with the known detailed structural information from NMR studies.

Preparation of 2-alkoxy-4-alkyl-5(4H)-oxazolones from mixed anhydrides of N-alkoxycarbonylamino acids

A general procedure for the preparation of 2-alkoxy-4-alkyl-5(4H)-oxazolones (AlkOx's) from N-tert-butoxy-, N-benzyloxy- and N-(9-fluorenylmethoxy)-carbonylamino acids has been devised. Purified mixed anhydrides are prepared from the parent acid and isopropenyl chloroformate and left in chloroform (Boc) for 24 h or dimethylformamide (Z, Fmoc) for 0.5-2 h. Symmetrical anhydride that may originate from disproportionation or reaction of AlkOx with hydrolyzed product is partially removed by extracting the AlkOx into petroleum ether. The products contain 0.5-30% of symmetrical anhydride.

Preparation of activated esters of N-alkoxycarbonylamino and other acids by a modification of the mixed anhydride procedure

Generation of a mixed anhydride using ethyl or isopropyl chloroformate and N-methylmorpholine in dichloromethane at room temperature, followed by addition of excess ring-substituted phenol or N-substituted hydroxylamine and a catalytic amount of tertiary amine, provides an efficient synthesis of activated esters.

Identification and suppression of decomposition during carbodiimide-mediated reactions of Boc-amino acids with phenols, hydroxylamines and amino acid ester hydrochlorides

N-tert-Butoxycarbonylamino acids (Boc-Xaa-OH) were coupled with p-nitrophenol (HONp) in dichloromethane using N,N'-dicyclohexylcarbodiimide (DCC) and N-ethyl-N'(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), and the products were identified and quantitated by high-performance liquid chromatography. Boc-Xaa-OH with Xaa = Val was coupled also with pentafluorophenol (HOPf) and hydroxy-containing additives (HOR), and the products were similarly determined as the methylamides. EDC-mediated reactions of Boc-Xaa-OH gave 8-25% of Boc-Xaa-Xaa-OR as well as Boc-Xaa-OR for R = Ph, Np, Pf, benzotriazole (Bt) and 5-norbornene-endo-2,3-dicarboxamide; DCC-mediated couplings, 5-7% for R = Np and Bt. No dimer was formed in couplings with N-hydroxysuccinimide or 3-hydroxy-4-oxo-3,4-dihydro-1,2,3-benzotriazine. Dimerization was eliminated from DCC-mediated reactions by the addition of 1 equiv. of N-methylmorpholine, from the EDC-mediated reactions by carrying them out in pyridine. Dimerization is attributed to formation of the intermediate 2-alkoxy-5(4H)-oxazolone that undergoes fragmentation to the N-carboxyanhydride, which reacts with the alcohol giving amino acid ester. Ester produces dimer by aminolysis of the O-acylisourea. Decomposition (1.4%) was also detected by analysis for H-Val-Phe-OMe in DCC-mediated reactions of Boc-valine with H-Phe-OMe, and was demonstrated to be caused by the hydrochloride of the ester salt that had been neutralized with N-methylmorpholine. Decomposition was eliminated by the addition of 5% of pyridine, which also had the beneficial effect of suppressing N-acylurea formation.

Dissociation kinetics of actinomycin D from oligonucleotides with hairpin motifs

The dissociation of 7-aminoactinomycin D (7-AM-ACTD) from d(ATGCATATGCAT), d(ATGCAT-T-ATGCAT), or d(ATGCAT-A-ATGCAT) at 20 degrees C cannot be adequately described by a single-exponential decay and requires a fit with two rate constants. The relative contributions of these two rate processes and their temperature dependence can be attributed to the coexistence of two conformational species in solutions. The slow dissociation rate corresponds to oligonucleotides in the dimeric duplex form, whereas the fast rate occurs with those in the hairpin conformation. The increased relative contribution of the faster component at higher temperatures is consistent with the more favorable thermal stability of the hairpin form. Studies with d(ATGCAT-TTT-ATGCAT) and d(ATGCAT-AAA-ATGCAT), which exist predominantly in the hairpin conformation, indicate that 7-AM-ACTD dissociates from these oligomers single-exponentially with rate constants comparable to or less than those obtained for the dimeric duplex of d(ATGCATATGCAT). Equilibrium binding titrations suggest that ACTD binds to hairpins as strongly as to the related dimeric duplexes, suggesting that the stacking geometry of the G.C base pairs at the dG-dC intercalating site of the hairpin stem is not greatly different from that of the dimeric duplex. The considerable variation in the dissociation rates of 7-AM-ACTD from hairpins, however, reflects the varying degrees of DNA minor-groove distortion of the stem duplex resulting from the hairpin loop formation and consequent interactions with the pentapeptide rings of ACTD. The plausibility of our interpretation is further supported by results from electrophoretic measurements, thermal melting profiles, and additional studies with hairpins containing a CGCG or GCGC stem.

Racemization during aminolysis of activated esters of N-alkoxycarbonylamino acids by amino acid anions in partially aqueous solvents and a tactic to minimize it

Racemization during the aminolysis of activated esters of N-alkoxycarbonylamino acids by amino acid anions in aqueous dimethylformamide was examined by determining the epimeric products by high-performance liquid chromatography. Partial racemization occurred for a variety of esters, particularly when sodium hydrogen carbonate was used to generate the anion of D-valine. The racemization results from prolonged contact of unconsumed ester with the alkaline medium. Variation of the stoichiometry of reagents for reactions with N-benzyloxycarbonylphenylalanine (Z-Phe) 4-nitrophenyl ester revealed that racemization could be minimized by using Na2CO3 as base and a 50% excess of amino acid anion. An efficient synthesis of optically pure Z-L-Phe-D-Val-OH was achieved with a reaction time of 15 min.

Studies on the disproportionation of mixed anhydrides of N-alkoxycarbonylamino acids

Mixed anhydrides from Z-valine and ethyl, isobutyl, isopropyl and isopropenyl chloroformate, and from N-tert-butoxycarbonyl- (Boc) and N-benzyloxycarbonyl- (Z) leucine and phenylalanine and Boc- and N-9-fluorenylmethoxycarbonyl-valine and ethyl chloroformate were purified and left in dichloromethane at 23 degrees C. The symmetrical anhydride (SyAn) generated after 24 h was determined by normal phase high-performance chromatography. No SyAn was produced from the anhydrides of Z- and Boc-valine; SyAn was produced from the other anhydrides. Anhydrides examined without isolation generally produced more SyAn than the pure compounds. More SyAn was generated in dimethylformamide and tetrahydrofuran than in dichloromethane, or in the presence of an excess of N-methylmorpholine or triethylamine. The anhydride from isobutyl chloroformate was much more stable than the anhydride from ethyl chloroformate. It is suggested that disproportionation of pure mixed carboxylic acid--carbonic acid anhydrides occurs by a bimolecular mechanism.

Studies on sensitivity to racemization of activated residues in couplings of N-benzyloxycarbonyldipeptides

A series of 24 peptides Z-Gly-Xaa(R)-OH where Xaa = 15 different residues and R = H, NH2, tBu, Bzl, Trt, Mtr, and StBu were coupled with valine benzyl ester in dimethylformamide or dichloromethane at +5 degrees. The accompanying racemization was determined by analysis of the epimeric products by normal phase high-performance liquid chromatography (HPLC) for Xaa(R) = Met, Cys(StBu) and Lys(Z) and by reversed-phase HPLC after removal of benzyl-based protecting groups for Xaa(R) = Ser(tBu), Thr(tBu) and Arg(Mtr). The coupling methods examined included mixed anhydride (MxAn) at -5 degrees, and N,N'-dicyclohexylcarbodiimide (DCC), benzotriazol-1-yl-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) and O-benzotriazol-1-yl-N,N,N',N'-tetramethyluroniumhexafluorophosp hate (HBTU) in the presence of 1-hydroxybenzotriazole (HOBt). Very few couplings gave stereochemically pure products. The order of sensitivity to racemization of residues depended on the method of coupling and the solvent. It varied most when comparing MxAn to HOBt-assisted reactions; it varied moderately when comparing HOBt-assisted reactions. There was less variation in comparing BOP and HBTU reactions that are initiated by the same mechanism. Leu, Nle, Phe, Asn, Lys(Z) and Asp(OBzl) are identified as the residues least sensitive to racemization. DCC-HOBt generally led to less epimerization than the other methods.

Binding specificities of actinomycin D to non-self-complementary -XGCY-tetranucleotide sequences

Studies on the binding specificity of actinomycin D (ACTD) to tetranucleotide sequences of the form -XGCY- have been extended to include the non-self-complementary sequences. ACTD binding characteristics are investigated by equilibrium, kinetic, and thermal denaturation for decameric duplexes d(ATA-XGCY-ATA)-d(TAT-Y'GCX'-TAT), where X and Y are complementary to X' and Y', respectively, but not to each other. The results indicate that when X = G or Y = C, the oligomers exhibit significantly weaker ACTD binding affinities, smaller melting temperature increases upon drug binding, and faster SDS-induced ACTD dissociation rates than the other sequences. Estimated binding constants at 18.5 degrees C for decameric duplexes containing -AGCA-/-TGCT-, -AGCG-/-CGCT-, or -CGCA-/-TGCG- are in the range of 4-9 microM-1, whereas for the ones containing -GGCT-/-AGCC-, -GGCA-/-TGCC-, or -GGCG-/-CGCC- they range from 0.6 to 2 microM-1. In contrast to the characteristic SDS-induced ACTD dissociation times of 600-1000 s for the stronger binding sites, the sequences containing X = G or Y = C exhibit at least an order of magnitude faster dissociation kinetics. These observations are further supported by the induced CD results and fluorescence measurements with 7-amino-ACTD. The findings from these non-self-complementary -XGCY- tetranucleotide sequences are consistent with those found earlier for the self-complementary counterparts, and they together clearly demonstrate that a base sequence alteration adjacent to the GC site can have a profound effect on the ACTD binding as well as dissociation characteristics, likely a consequence of subtle conformational alterations near the binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

N-alkoxycarbonyl-glutamic and aspartic acids. Studies on the activation and cyclodehydration and side-reaction encountered in analysis of glutamic acid using Fmoc-chloride

N-Alkoxycarbonylaminodicarboxylic acids were reacted in dichloromethane with N-ethyl-N'-(dimethylaminopropyl)carbodiimide hydrochloride, and with methyl chloroformate in the presence of N-methylmorpholine. Removal of secondary products by washing the mixtures with aqueous solutions gave good yields of the pure crystalline internal anhydrides. Anhydrides of N-benzyloxycarbonyl- (Z) and N-9-fluorenylmethoxycarbonyl-(Fmoc) L-glutamic and L-aspartic acids and of N-tert.-butoxycarbonyl-L-aspartic acid were prepared in this way. The compounds were shown to be amenable to normal phase high-performance liquid chromatography (NP-HPLC) on a CN-column using tert.-butanol-hexane as solvent. The products of the reactions of Z- and Fmoc-glutamic acid with hot acetic anhydride were examined by nuclear magnetic resonance and NP-HPLC before and after methanolysis in an attempt to establish if any of the corresponding pyroglutamates were formed. The reaction of Fmoc-chloride with Fmoc-glutamate was examined for the same reason. It is concluded that the side product generated during the reaction of Fmoc-chloride with glutamic acid which is used for analysis of the latter is the N-protected internal anhydride and not the pyroglutamate as reported in the literature.

Sr2+ facilitates intermolecular G-quadruplex formation of telomeric sequences

Electrophoretic and spectroscopic studies were made with the telomere-related sequences d(G4T2G4T2G4T2G4) (T2) and d(G4T4G4T4G4T4G4) (T4) in the presence of Na+, K+, and Sr2+. Electrophoretic evidence indicates that these two oligomers exist in multiconformational states in solutions. A band identified as that of intermolecular (tetramolecular) G-quadruplex is apparent in both T2 and T4, whereas a band identified as intramolecular (monomeric) G-quartet is only evident in T4. The remaining electrophoretic bands that exhibit mobilities intermediate of these two extremes are identified as those of hairpin-related duplexes and tetraplexes. In the presence of millimolar concentrations of Sr2+ and subsequent thermal treatment, the intensity corresponding to the band attributable to the intermolecular G-quadruplex is dramatically enhanced in T2 while those of the hairpin-related bands of intermediate mobility are greatly reduced. Similar but less dramatic enhancement of the intermolecular quadruplex band is also observed in T4. Although these effects can also be induced by K+, orders of magnitude higher concentrations are needed. The intensity of the intramolecular G-quartet band, apparent in T4 but not in T2, appears to be relatively insensitive to the type of cation present in the solution. These results demonstrate that both Sr2+ and K+ facilitate the intermolecular G-tetraplex formation, with the divalent cation being much more effective. Comparison with the corresponding CD spectral characteristics suggests that the electrophoretic intensity enhancement of the intermolecular G-quadruplex band is correlated to the intensity enhancement of of the positive CD maximum at 265 nm.(ABSTRACT TRUNCATED AT 250 WORDS)

[Experimental study on early multiple organ failure after severe burns]

Forty-three male mongrel dogs (12.5 +/- 2.5 kg) were divided into normal control (n = 7), immediate infusion (n = 8), non-infusion (n = 13) and delayed infusion (n = 15) groups. A 50% TBSA third degree surface burn was produced by igniting 3% napalm for 30 seconds on the shaved back. Cardiac, pulmonary, hepatic, renal and gastrointestinal functions were monitored following the thermal injury. The findings of these studies showed that mean arterial pressure, cardiac index, left ventricular work, right ventricular work, ADP/O ratio and ATP were all significantly decreased (P less than 0.05). However pulmonary artery wedge pressure, pulmonary vascular resistance, systemic vascular resistance, P(A-a)O2, Beef, Cr, UN, ALT, LDH, TB, DB, and MDA were markedly increased (P less than 0.05). Severe shock occurred soon after burns. Thirteen dogs died within 12 hours in the non-infusion group. All the dogs were resuscitated when immediate infusion of lactic acid Ringers solution was given according to Parkland formula, and all of them tide over shock stage smoothly without obvious changes in visceral functions. However, dogs were not resuscitated when infusion was delayed 6 hours postburn. The changes in visceral were even more severe in this group than those in non-infusion group. These results demonstrated that delayed resuscitation was an important factor of MOF in the early postburn stage. The marked increase in MDA in the myocardiac, lung, liver, renal and gastrointestinal tissues indicated that lipoperoxidation by free oxygen radicals was closely related with visceral damages.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical study of transforming growth factor-alpha in human lung cancers

The expression of transforming growth factor-alpha (TGF alpha) was assessed by immunohistochemical staining in 52 human lung tumor samples. All of the 8 small cell lung cancers were negative whereas all of the 18 adenocarcinomas and 23 of the 26 squamous cell carcinomas showed positive immunoreaction to TGF alpha. Distribution of TGF alpha stainings in the squamous cell carcinomas was weaker and more heterogeneous as compared to the adenocarcinomas. Ultrastructural localization of TGF alpha in the squamous cell lung carcinomas by indirect immunogold staining revealed that TGF alpha is present in the cytoplasm as well as the cell membrane but not in the nucleus. This suggests that the lung cancer cells are not only the producer of TGF alpha, but also the target cells of the TGF alpha action. The expression of TGF alpha in lung tumors may be useful diagnostically in differentiating small cell lung cancer from non-small cell lung cancer and may also be important in the study of the biological properties of primary lung cancers.

Studies on asymmetric induction associated with the coupling of N-acylamino acids and N-benzyloxycarbonyldipeptides

The asymmetric induction occurring during aminolysis by an amino acid benzyl ester of the 5(4H)-oxazolones obtained from N-acyl-DL-valine for acyl = formyl, acetyl, benzoyl, trifluoroacetyl and N-benzyloxycarbonyl-Xaa where Xaa = Gly, Ala and Leu in dichloromethane and dimethylformamide at +5 degrees and -5 degrees was determined by analysis of the epimeric products by high-performance liquid chromatography after removal of protecting groups by hydrogenolysis. The influence of the side-chain of the activated residue on induction was assessed by examining aminolysis of the 5(4H)-oxazolones from N-benzyloxycarbonyl glycyl-Xaa-OH for Xaa = Ala, Leu, Val, and Phe. The contribution of induction to the epimeric content of products obtained from couplings mediated by N,N'-dicyclohexylcarbodiimide in the presence and absence of l-hydroxybenzotriazole, and by the mixed-anhydride method, were calculated. The induction was affected at varying levels by the nature of the N-acyl group, the side-chain of Xaa, the nature of the aminolyzing nucleophile, the nature of the solvent, and the temperature, with diastereomeric excesses reaching -32 and +53. The influence of the side-chain of Xaa on the induction was different in the two solvents. For the N-acyl series, the epimeric content of products did not always correctly reflect the relative tendencies of the derivatives to racemize. The order for epimeric content of the products also depended on the method of coupling.

Reaction mechanisms in peptide synthesis. Part 2. Tautomerism of the peptide bond

We had concluded in previous work that ring opening of a 2-alkyl-5(4H)-oxazolone by water or ammonia leads to transient high-energy imidol intermediates which instantly tautomerize to the native amides. Using the MOPAC molecular orbital program, detailed geometric and energetic characteristics of the tautomerism of a peptide bond have been determined on the AM1 level. The results demonstrate that tautomerism of a peptide bond comprises a three-stage process involving three successive transition states and a bimolecular mechanism: (i) E----Z peptide bond isomerization followed by dimerization, (ii) concerted double-hydrogen exchange leading to an alpha-hydroxyimine (imidic acid) followed by splitting of the dimer, and (iii) Z----E N-methylimine inversion. While pathway (iii----ii----i) is predicted as a feasible route terminating in the formation of a peptide bond, the inverse route (iii----ii----i) is excluded as a possible initial step in the generation of a 5(4H)-oxazolone intermediate.

Reaction mechanisms in peptide synthesis. Part 1. Semiquantitative characteristics of the reactivity of 2-methyl-5(4H)-oxazolone with water and ammonia in the gas phase and weakly polar media

2,4-Dialkyl-5(4H)-oxazolones are well-recognized intermediates in some aminolysis reactions in peptide synthesis. Using the MOPAC molecular orbital programs, detailed geometric and energetic characteristics of the elementary reaction pathways for the additions of water and ammonia to 2-methyl-5(4H)-oxazolone have been determined at the AM1 level. The results demonstrate that the additions must be parsed into a two-step mechanism involving formation of the alpha-hydroxyimine followed by tautomerization to the parent N-acetylamino acid or amide.