Search

From thirty three new optically active 1,5-benzodiazepine derivatives the UV and CD data are reported and the bands discussed related to corresponding electronic transitions respectively stereochemical features.

From forty one chiral benzodiazepin-2-ones the UV and CD data are reported and the bands discussed with respect to corresponding electronic transitions respectively stereochemical features.

A route to optically active variously substituted 4-methyl- and 4-methyl-7-substituted 1,3,4,5-tetrahydro-2H-1,5-benzo-diazepin-2-ones as analogues of commercially available Lofendazam (7-chloro-5-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one, 1) was developed. Fortyone variously substituted optically active compounds having the same configuration were prepared and the UV and CD spectra of the parent compounds bearing no additional substitution in the benzene ring are discussed.

Syntheses of 5α-cholesteno[3,2-d]- (5a), [2,3-d]- (12a), and [3,4-d]pyrimidines (15a) have been achieved by using hydroxymethylene derivatives of relevant cholestanones prepared from cholesterol (1). Their CD spectra exhibit at least three Cotton effects between 300 to 200 nm, a first CD band around 290, a second one around 260 and a third one around 220 nm. A quadrant rule is developed and applied to the determination of the sign of the first CD band, while a helicity rule is applicable to the third CD band. The first band is positive in the [3,2-d] series, whereas it is negative in the [2,3-d] and the [3,4-d] series. The third band is negative in all three series.

The correlation between the absolute configuration and CD of aza- and thiaflavanone (1, 2) is discussed: the 2R configuration for the laevorotatory enantiomers has been established by a comparison of their CD data with those of (S)-(−)-3. For the Cotton effect within the n π* band of 1 and 2 the same helicity rule is valid as for the homochirally analogous flavanones (3). Starting from (S)-(−)-flavanone (3) and cholesterol (5), we have synthesized the chromane derivatives 4 and 20, respectively. The 1Lb band of the chromane chromophore has been unequivocally identified in the range between 255 and 290 nm in the CD spectra of 4 and 20. For this Cotton effect the opposite helicity rule is valid as compared with the homochirally analogous tetralins: the P/M helicity of the hetero ring leads to a negative/positive CD within the 1Lb band. The modification of the helicity rule can be explained with the help of Petruska's “q values”.

Chiroptical properties of the title compounds have been studied. The influence of the substitution pattern of the aromatic moiety and the consequence of the amide → thioamide conversion are discussed as well.

From forty one chiral benzodiazepin-2-ones the UV and CD data are reported and the bands discussed with respect to corresponding electronic transitions respectively stereochemical features.

The thermal unfolding of cytochrome P-450 LIN and P-450 CAM measured in presence and absence of their specific substrates was analyzed by circular dichroism (CD) and the α-helix content was estimated. Both proteins show, independent of the presence or absence of the substrates, nearly the same amount of loss of the CD in the peptide region. The comparison of the half transition temperature determined from different chromophores and different methods indicates a non-two-state transition of the thermal unfolding. For such analysis we developed a new spectrometer, which is capable of measuring the CD simultaneously at all wavelengths in a limited wavelength region.

Starting from cholesterol the three possible stereoisomeric 1,4-benzodioxanes 24, 31, 32 and a series of analogues with 2βH,3βH configuration (25–27, 29, 30) have been synthesized. The α band of the 1,4-benzodioxane chrompohore has been unequivocally identified in the CD spectra between 325–300 nm. For its Cotton effect the same helicity rule is valid as for homochirally analogous tetralins: the P/M helicity of the heteroring leads to a positive/negative CD within the α-band. The (2′R,3′R) configuration of 6 has been established by a comparison of its CD data with those of 39 and with the help of the above-mentioned helicity rule. This allows the assignement of the (2S,2′R,3′R) configuration of (−)-silandrin (3).

Some oximes and oxime acetates of transoidal cholestenones have been synthesized. In three cases of stable syn/anti pairs of oximes both stereoisomers could be separated. The CD-spectra of all compounds have been measured. All syn-isomers show an additional CD band around 280 nm, which does not exist for anti-oximes.

The absolute configuration of the 2-(phenylmethyl) pyridine derivatives 1-9 had been established by X-ray diffraction and chemical correlation. Their CD spectra have been studied in different solvents for the free and protonated forms. It has now been found that, from the sign of the strong CD couplet between 270 and 220 nm, which was observable for all these compounds besides 7 and 9, their absolute configuration can be determined much quicker

A new, very convenient and sensitive “in situ” method has been developed for the determination of the absolute configuration of chiral compounds, which can bind to the axial position of [Rh2(O2CCF3)4] (5) and induce circular dichroism within its electronic absorption bands. The CD spectra of the “in situ” complexes of chiral alcohols, ethers (including epoxides), olefins, and ketons with 5 show up to 5 Cotton effects (A – E) in the 600 – 300 nm range. This method works well for chiral secondary alcohols and monoolefins. For these compounds tentative rules are proposed, which correlate the absolute stereochemistry with the sign of certain Cotton effects of their complexes. A rule for the sign of band E for alcohols and a quadrant rule for the sign of band C for olefins can be applied. Olefins induce unexpected strong Cotton effects in presence of 5 giving evidence for a relatively stable π-bond between olefin and rhodium atom.

Some oximes of 4- and 6-ketosteroids, of des-A-5-keto-steroids, and the related compounds 31 and 33 have been synthesized. In three cases stable B / Z pairs are formed which could be separated. The CD-spectra of all compounds have been measured. The Cotton effects around 217 run of the 6-hydroxyimino-5α-steroids (1 – 18, 34, 36) are negative, those of the corresponding 4-analogues (20 – 23) are positive. A similar relationship holds for the des-A-steroidoximes 24 – 26 vs. 27, and the syn-oximes 34/36 vs. their anti-analogues 35/37. This Cotton effect can, therefore, be used for the determination of the configuration of such oximes. The Cotton effects below 200 nm do not always show similar regularities.

The relationship between structure and circular dichroism was studied for a series of cardenolides including some compounds with saturated lactone ring.

The first CD spectra of optically active ferricinium salts are reported. Cotton effects corresponding to the metal-ligand charge-transfer band have been observed for the compound with planar chirality.

The CD of ketoximes of defined (E)/(Z configuration and some of their O-derivatives of steroids (4-en-3-ones, 4-en-6-ones, 5-en-7-ones, 4,6-dien-3-ones) and monoterpenoids (verbenone, carvone) have been investigated. All show two Cotton effects around 250 nm (band II) and 230 nm (band III), which usually have opposite signs. For the first-mentioned one a rule is proposed for the correlation between CD and absolute configuration. Most of the (Z)-oxime derivatives give an additional Cotton effect around 290 nm (band I), whose sign is always opposite to that of band II.

Synthesis of Medium and Large Rings, XXVII1. - Chromatographic Separation of the Enantiomeric 3.6-Heptanophthalides. - A Contribution to the Problem of the Absolute Configuration of [nJ Paracyclophanecarboxylic Acids The partial chromatographic separation of the racemic title compound 1 (ee = 40%) was achieved on triacetylcellulose with ethanol using a recycling technique. Comparison of the CD spectra of (+)22365-1 with (+)22365-2 leads to the absolute configuration (P) for both compounds. This assignment is of interest in view of earlier configurational assignments for [n]paracyclophanecarboxylic acids.

The 1 B 2u -band CD of siccanin ( 3 ) and some of its derivatives obeys the known rules for the benzene chromophore with the appropriate substitution pattern. The CD spectrum of the chromanone 8 is better resolved than that of related flavanones, the band between 300–320 nm is most probably the 1 B 2u -band of this chromophore. The non-planar styrenes 10–12 symmetrically substituted in the benzene ring with respect to the “pivot” bond follow Crabbe's rule, and the absolute configuration of siccanochromene-A ( 13 ) in the chromene ring follows from its CD to be S .

Several Cotton effects are developed within absorption bands of trinuclear organotransitionmetal complexes in the presence of acids, diols, amines and aminoalcohols even in the case of bulky substituents on nitrogen; with monohydroxy compounds no circular dichroism could be detected.

(+)- and (−)-1 (N,N,N′,N′-Tetramethyldithiooxamide) were enriched by semipreparative liquid chromatography on triacetylcellulose. According to1HNMR in the presence of an optically active auxiliary, the sample of (+)365-1 had an enantiomeric purity of 0,50±0,01, thus permitting to calculate the CD spectrum for the pure enantiomer. The CD and UV spectra are discussed in terms of qualitative MO theory. Thereby, the absolute configuration of (+)365-1 is determined to be (R).

Resume Die zwei Phenylchromophore eines optisch aktiven 1,2-disubstituierten 1,2-Diphenylethans geben unabhangig voneinander Cotton-Effekte innerhalb des Wellenlangenbereichs der α-Bande. Durch Bildung der Summen-und Differenz-CD-Kurve fur ein threo/erythro Paar erhalt man CD-Spektren, die fur jedes “Halbmolekul” charakteristisch sind, und die im allgemeinen zwei 0-0—Linien um 37230 cm -1 aufweisen. Aus deren Vorzeichen kann die absolute Konfiguration an jedem der Chiralitatszentren eindeutig bestimmt werden.

The syntheses of two new ring systems, 5α-cholest-2-eno[3,2-e]-(6) and 5α-cholest-2-eno[2,3-e]-as-triazine (11) are described. While the reaction of diketone 1 with semicarbazide hydrochloride results selectively in derivatives of 6, S-methylisothiosemicarbazide under basic conditions affords the other possible ring closure product 11. An unequivocal decision between both types was made by X-ray analysis of compound 9. Comparison of the UV and CD spectra shows that besides the two absorptions appearing in the UV spectra additional ones can be observed in the CD, which may be assigned to further n – π* or only slightly allowed π – π* transitions. Synthese, Rontgen-Strukturanalyse und CD von Cholesteno-as-triazinen1) Die Synthesen von zwei neuen Ringsystemen, 5α-Cholest-2-eno[3,2-e]- (6) und 5α-Cholest-2-eno[2,3-e]-as-triazin (11) werden beschrieben. Wahrend das Diketon 1 mit Semicarbazid-hydrochlorid selektiv zu Derivaten von 6 reagiert, ergibt S-Methylisothiosemicarbazid das andere mogliche Ringschlusprodukt 11 unter basischen Reaktionsbedingungen. Zwischen den beiden Typen konnte mit Hilfe einer Rontgen-Strukturanalyse von 9 unterschieden werden. Vergleich der UV- und CD-Spektren zeigt, das auser den zwei Absorptionen, die im UV-Spektrum auftreten, zwei andere in den CD-Spektren beobachtet werden, die weiteren n – π*- oder nur wenig erlaubten π – π*-Ubergangen zugeordnet werden konnen.

The complexes of formula [CuSu 2 Am 2 * ] formed in situ from amino steroids (Am * ) and a methylene chloride solution of the complex [CuSu 2 Pr 2 ] (Su: succinimidate; Pr: isopropyl amine) show in the range of the d-d bands two Cotton effects at approx. 700 (Band I) and 600 nm (Band II), whose signs are correlated with the preferred torsion angle of the H 2 N-Cu moiety: a positive torsion angle leads to a positive CD-band I and to a negative CD-band II. These complexes form useful Cottonogenic derivatives of primary amino compounds.

Although chiroptical methods have been used in chemistry for some 150 years, and the basic theory was developed by Rosenfeld 50 years ago, their success in determining absolute conformation rests mainly on empirical rules. Some of these can be proved theoretically; however, in the case of more complex molecules this is not yet always possible. In what follows, an attempt is made to bridge the wide gap between theory and empiricism: “qualitative MO-theory”, which has already been successfully used to explain reaction mechanisms, the shape of molecules, or photoelectron spectra, can also be applied to circular dichroism (CD). In general we shall have to be content with a reasonable interpretation of the experimentally determined sign correlation, but even this will be of great value since it can yield general relations between the geometry of molecules and the sign of CD. Such relations become particularly important when only a few examples of a given chromophore are known. If first and second sphere of a molecule are achiral then sector rules can be put forward, and in other cases helicity or chirality rules.

Several optically active 1,2-di- and 1,3,5-trisubstituted benzene derivatives have been synthesized, in which one substituent is chiral, the others being methyl, ethyl, or neopentyl. The CD spectra within the α-band can be explained well by making use of Platt and Petruska's q values. While introduction of OH at the benzylic position of a substituent inverts the direction of the corresponding electric transition moment vector in the plane of the ring, this has no such influence upon the magnetic transition moment perpendicular to the ring. Circulardichroismus, XCI: — Synthese und CD von Benzolderivaten mit Mehreren ahnlichen Substituenten Mehrere optisch aktive 1,2-di- und 1,3,5-trisubstituierte Benzolderivate, in denen ein Rest chiral ist, die anderen Methyl, Ethyl oder Neopentyl sind, wurden dargestellt. Die CD-Spektren innerhalb der α-Bande lassen sich unter Verwendung der von Platt und Petruska eingefuhrten q-Werte gut deuten. Wahrend die Ein-fuhrung von OH in benzylischer Position eines Restes zur Richtungsumkehr des zugehorigen elektrischen Ubergangsmoments in der Ringebene fuhrt, hat dies auf das entsprechende magnetische Ubergangsmoments senkrecht zum Ring keinen solchen Einflus.

A comparison of the CD- and UV-spectra of benzene derivatives, which are mono-, 1,4-di- or 1,3,5-trisubstituted by (identical) chiral ligands, revealed that the rotational strength within the α-band of mono- and 1,3,5-trisubstituted benzenes is mainly derived from the magnetic transition moment of the benzene chromophore perpendicular to the ring, and from a corresponding electric transition moment stolen from a ligand transition. For the 1,4-disubstituted homologues, the main contribution to the rotational strength is associated with the electric transition moment in the plane of the benzene chromophore and with a corresponding magnetic transition moment, stolen from the A1g E1g (D6b-notation) transition within the same ring. For the 1,3,5-trisubstituted compounds, the 0–0-band is scarcely, or not at all, detectable in the UV-spectra, but distinctly recognizable in the CD-spectra. In a few cases Cotton-effects between the positions of the α- and the p-bands could be detected, which are ascribed to the magnetically allowed A1g E1g (D6b-notation) transition.

The CD spectra of 48 colchicine alkaloids and of some of their derivatives were given. The effects of the substituents and of the basic skeleton on the chiroptical properties of the measured compounds were discussed.

General interpretation of chiroptical characteristics of binding process of prochiral (Z) and chiral (Z ∗ ) 1,4-benzodiazepin-2-ones to human serum albumin (HSA) is presented. Interpretation of binding of Z studied by circular dichroism (CD) measurements allows us to conclude that the CD within the bands of bound Z is mainly due to the chirality of the first sphere and that the greatest part of 3 is bound in the M-conformation. For Z ∗ we conclude that ( S )-1 binds on both binding sites of HSA in the M-conformation, while ( R )-1 binds on two different binding sites in opposite conformations. Furthermore we conclude that binding via two nitrogens of the benzodiazepine, i.e. at two ends of the chromophoric system is rather more probable than via ring A.

The sign of the CD within the first absorption band (200–220 nm) of optically active vinyl-cyclopropanes has been correlated with the absolute conformation of the chromophore in a non-empirical way. A positive torsional angle between the C=C and the bisectrix of the cyclopropane ring between 0° and ≃ + 70° gives a positive Cotton effect; between ≃ + 110° and 180° it gives a negative one. The rule has been tested mainly on models of terpenoid origin.

Cyclische Anhydride zeigen zwei bis vier Cotton-Effekte unterhalb von 260 nm. Mit Hilfe der qualitativen MO-Theorie lassen sich Voraussagen uber den Zusammenhang zwischen absoluter Konformation und Vorzeichen der ersten beiden CD-Banden fur solche Anhydride mit inharent achiralem und inharent chiralem (C2-Symmetrie) Chromophor ableiten. Bei ersteren haben die beiden langstwelligen CD-Banden gleiches Vorzeichen, dafur gilt die Sektorregel mit 12 Sektoren der Abbildung 5. Fur den Anhydridchromophor mit C2-Symmetrie gilt eine Helizitatsregel: Ein negativer Interplanarwinkel zwischen den beiden Ebenen der C = O-Gruppen fuhrt zu einem negativen Cotton-Effekt um 240 nm und zu einem positiven um 220 nm. Circular Dichroism, LXXIII1). - Chiroptical Properties of Cyclic Anhydrides Cyclic anhydrides exhibit two to four Cotton effects below 260 nm. Applying qualitative MO theory leads to predictions about the correlation between absolute conformation and signs of the first two CD bands for such anhydrides with an inherently achiral or inherently chiral (C2 symmetry) chromophore. For the first, the two CD bands at longest wavelengths have the same sign and conform with the sector rule of figure 5 with 12 sectors. For the anhydride chromophore with C2 symmetry a helicity rule holds: A negative interplanar angle between the two planes of the C = O groups leads to a negative Cotton effect around 240 nm and to a positive one around 220 nm.

The pH-dependence of the 1H NMR and Circular Dichroism (CD) spectra of 2-methylsuccinic acid was investigated. Both spectra undergo dramatic changes between pH 4 and 6, where both carboxylic groups become ionized. From the coupling constants of the tertiary proton with the assigned1 diastereotopic methylene protons, it is concluded that below pH 4 the syn-clinal (2) and above pH 6 the anti-periplanar (1) conformation of methylsuccinic acid prevail. The diesters of methylsuccinic acid also assume mainly the syn-clinal conformation (2). The pH-dependence of the CD spectra is discussed in terms of conformation and/or ionization effects.

The CD of saturated iridoids containing a 2.9-dioxatricyclo[4.3.1.03,7] decan skeleton derived from valepotriates is determined by the acetal chromophore. For the less symmetric ring system of 1,6-anhydro hexapyranoses the sign of this CD is predictable. The vicinal effect for enones and diketones in this series is appreciable. A new rule for the correlation between the CD around 190–205 nm of enol ethers and their absolute conformation is given; the same reasoning is applicable to explain the known rules for cisoid and transoid vinyl cyclo-propanes.

The absolute configuration of dechlorogilmaniellin (2) could be determined from its chiroptical data by applying coupled-oscillator theory to the CD couplet around 272 nm and from the sign of its n π*Cotton effect. Gilmaniellin (1) has the same absolute configuration.

Ausgehend von Cholesterin wurden die drei moglichen stereoisomeren Isochromane 10–12 synthetisiert, die durch Oxidation die entsprechenden Lactone 13–15 ergaben. Die n π*-Bande des Isochromanon-(„Benzoesaureester”-)Chromophors konnte in den CD-Spektren zwischen 245 und 265 nm eindeutig identifiziert werden. Fur ihren Cotton-Effekt gilt die gleiche Helizitatsregel wie fur homochiral analoge 1-Tetralone: sein Vorzeichen sowie das des Cotton-Effekts innerhalb der α-Bande des sonst unsubstituierten Benzolchromophors ist entgegengesetzt zum Vorzeichen des Torsionswinkels (O)CC(Ctransoid); das Vorzeichen des Cotton-Effekts innerhalb der ”Konjugationsbande” ist gleich dem dieses Torsionswinkels. Der Zusammenhang zwischen absoluter Konfiguration und CD naturlicher Isochromanonderivate wird diskutiert: nur fur den Cotton-Effekt innerhalb der n π*-Bande ist die genannte Helizitatsregel von der Benzolring-substitution unabhangig. Die Ungultigkeit der Helizitatsregel chiraler Tetraline fur homochiral analoge Isochromane kann mit Hilfe der „q-Werte” von Petruska erklart werden. Circular Dichroism, LXXXI. - Synthesis and Circular Dichroism of Steroids with an Isochromanone Chromophore Starting from cholesterol the three possible stereoisomeric isochromanes 10–12 have been synthesized; their oxidation gave the corresponding lactones 13–15. The π* band of the isochromanone („benzoic acid ester”) chromophore could unequivocally be identified in the CD spectra between 245 and 265 nm. For its Cotton effect the same helicity rule is valid as for homochirally analogous 1-tetralones: its sign, and also that of the Cotton effect within the α band of the otherwise not substituted benzene chromophore, is opposite to that of the torsional angle (O)CC(Ctransoid); the sign of the Cotton effect within the „conjugation band” is the same as that of this torsional angle. The correlation between absolute configuration and CD of natural isochromanone derivatives is discussed: only for the Cotton effect within the n π* band the mentioned helicity rule is independent of the substitution of the benzene ring. The invalidity of the helicity rule of chiral tetralins for homochirally analogous isochromanes can be explained with the help of Petruska's „q values”.

Hydrogenation of the ketone group in di-O-benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼40%, d. e. at −60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature-dependent CD spectra of its acetyl congeners 18 and 19. X-Ray structure analysis of 7-O-acetylderivative (13) of 11 revealed the (R)-configuration at C(7). Two crystallographically independent H2O molecules are involved in the H-bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)-]C(161)-C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)-C(12) bond (torsional angle [C(11)-]C(12)-C(121)[C(161)] is −93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic-acid lactone) derivatives from the 6-membered lactone derivative 20, studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and nπ* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.

Cottonogenic in situ derivatives of potential ligands with different transition metal complexes containing 2 or 3 metal atoms have been used for the purpose of 1) obtaining CD-bands from non-absorbing compounds, and 2) to force flexible molecules into one preferred conformation. Natural products whose stereochemistry can be investigated in this way are e.g. acids, glycols, amines, aminoalcohols, diamines, peptides and nucleoside derivatives. From the Cotton effects the absolute conformations or even absolute configurations can be obtained with the help of empirical rules.

The circular dichroism of keto derivatives with trichothecane skeleton and some of their rearrangement products has been measured. The sign (and sometimes even the magnitude) of all COTTON effects can be explained by applying the respective rules for the cyclohexanone, cyclopentanone, enone and ene-ester chromophores. Thus conformations could also be determined in those cases which did not follow unambiguously from conformational analysis. The conformation of the muconic acid moiety of the macrocyclic ring of verrucarin A is the same in dioxane solution as in the crystalline state.

Ausgehend von 4.8-Dioxo-adamantan-carbonsaure-(2) (1) wurden einige solche monosubstituierte Adamantandionderivate in optisch aktiver Form neu dargestellt, deren Substituenten π-Elektronensysteme enthalten. Der CD dieser Diketone folgt im Prinzip der Oktantenregel. In einigen Fallen treten aber betrachtliche Vicinaleffekte auf. Circular Dichroism, LII. Synthesis and Circular Dichroism of some β-Substituted Adamantanones, III Starting from 4.8-dioxoadamantane-2-carboxylic acid (1) such monosubstituted adamantanediones have been newly prepared in optically active form, which contain π-electronic systems in the substituent. In general the CD of these diketones follows the octant rule. In some cases strong vicinal effects have been observed, however.

The preferred conformations of the C-acetyl groups of 1,3-seco-2-norestran-4-one's were determined by the circular dichroism method at different temperatures. The experimental results agree with the predictions based on conformational analysis. At low temperature the mono and dibromo ketones (1c) and (3a) have a bromine atom syn-periplanar relative to the CO bond.

The C=N-group of azomethines shows a weak absorption band approximately at 250 mμ which is optically active when the chromophore is placed into an asymmetric environment. Correlations between the circular dichroism of some steroidal cyclic azomethines and their stereochemistry are discussed.

The effect of deprotonation and alkaline denaturation on the conformation of DNA from various sources has been investigated by optical rotatory dispersion and circular dichroism measurements. Upon transition to alkaline pH, changes in the optical rotatory dispersion at the characteristic peaks around 228 and 290 nm are observed. The variation of the optical rotations in case of A. T-rich DNA is more pronounced than in case of G . C-rich DNA. For G . C-rich DNA, changes of rotations are mainly observed at pH values beyond 11.5; the transition ranging between pH 11.6 and 11.7. The transition is accompanied by a shift of the “cross-over” point towards longer wavelengths presumably due to deprotonation of guanine residues. Native DNAs show characteristic differences in their circular dichroism spectra dependent on the G · C content. Increasing the temperature (below the melting region) reveals enhancement of the circular dichroism band of native DNA around 270 nm whereas the opposite effect is found in the denatured state. As a possible explanation an increase of the chirality in the native helical DNA structure or a structure of intermediary character is considered. Titration up to pH 12 or higher produces a drastic increase of the rotational strength around 228 nm as well as changes in the other two circular dichroism-maxima which may be correlated to a diminuition of the chiral and helical structure.

– The circular dichroism of some non-conjugated unsaturated carbonyl compounds, which are conformationally mobile, has been measured at +20° and at about −178°. Specifically for the steroidal compounds 1 and 2 and the monocyclic aldehyde 14, their substituted analogs 4–6, 9–11, and 15–19, respectively, as well as for the aliphatic ketone 21 the CD. temperature gradients are interpreted in terms of the preferred conformations. In the case of the β,γ-unsaturated aldehydes 1 and 14, a correlation of these results with the photolytic decarbonylation from the excited singlet states is discussed.

The conformation of the cyclopentenones 5 to 8 is determined from their CD-spectra. The site of enolization and the conformation of cis - and trans -isohumulone ( 1 and 2 ) is determined with the help of the CD-spectra, the direction of enolization for the humulinic acids 3 and 4 is tentatively determined by the same method.

CD properties of three cyclo-γ-oligoglutamic acids and their t-butyl esters are reported. The assignments of the different Cotton effects are discussed. The CD of the cyclodipeptide is interpreted on the basis of a conformation with two trans amide groups in anti positions. A phenomenological correlation between chiroptical properties and conformation is presented for the other cyclooligopeptides.

The circular dichroism of several 2-amino tetralols-1 and 2-amino indanols-1 has been correlated with the absolute configuration of these compounds. For the CD of the 1Lb,-band of tetralins and heterocyclic analogues with chiral second sphere a rule is proposed to predict the sign. In 2-amino indanols-1 the sign of the CD-bands is determined by the stereochemistry at C-2 and not by that of the OH-group at C-1, which fact is explained on the basis of the same rule.