Conformations of cycloheptane

Bocian, David F.; Pickett, H. M.; Rounds, Thomas C.; Strauss, Herbert L.

doi:10.1021/ja00837a001

Cited by 154 publications

(79 citation statements)

References 5 publications

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“…The symmetry coordinates O, p (Bocian, Pickett, Rounds & Strauss, 1975) and q,, ~P2; qs, ~o~ (Cremer & Pople, 1975) (Table 1), then permutational isomers . :,/ ..... ,~ (k) occur at ¢,*2(B,TB) = ¢,~(B,TB) + 7rk/7 for k = 0-13.…”

Section: For the Symmetrical Forms Tc C Tb B [(Ix)-(xii)] Of O'clomentioning

confidence: 99%

“…Twist-chair (TC) C2 Chair (C) C, (IX) (X) Bocian et al (1975) and Bocian & Strauss (1977a) describe the four-dimensional hypersurface in terms of two mutually perpendicular tori. The C-TC pseudorotation follows a helical pathway on a torus of major radial coordinate q~3 and minor radial coordinate q~2.…”

Section: Introductionmentioning

confidence: 99%

“…However, for the C~.-and Q-symmetric conformers there are only 14 permutations/inversions in each case. If we define the 'origin' chair (C) and twist-chair (TC) conformers at ~o~(C)= 0, q~(C)= ~-and ~o~(TC)= rr/2, q~(TC)= rr/2 (Table 1), then permutational isomers (k) will occur (Bocian, Pickett, Rounds & Strauss, 1975;Bocian & Strauss, 1977a;Boessenkool & Boeyens, 1980) (Hendrickson, 1967)…”

Section: Introductionmentioning

confidence: 99%

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Symmetry-modified conformational mapping and classification of the medium rings from crystallographic data. II. exo-unsaturated and heterocyclic seven-membered rings

Allen¹,

Howard²,

Pitchford³

et al. 1994

Acta Crystallogr Sect B

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Crystallographic results derived from the Cambridge Structural Database (CSD) have been used to perform a systematic conformational analysis for methylenecycloheptane, oxocycloheptane, azocycloheptane, oxepane, azepane and for the e-lactone and e-lactam fragments. Conformational mappings based on symmetry-adapted deformation coordinates and principal component scores show that ring conformations in these fragments fall almost exclusively on the chair-twist-chair pseudorotation pathway. Symmetry-modified Jarvis-Patrick clustering has been used to generate conformational classifications in a semi-automated manner. A manual classification was preferred for the oxocycloheptanes due to wide conformational diversity within a rather small data set. Energy calculations have also been carried out for these systems using force-field methods and a novel conformation-hunting algorithm that attempts to locate all local minima without recourse to ring cleavage and reformation. There is good qualitative agreement between the crystallographic observations of conformation and the calculated features of the potential energy hypersurface, despite the wide variety of substitution patterns covered by the crystallographic results.

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Section: For the Symmetrical Forms Tc C Tb B [(Ix)-(xii)] Of O'clomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Symmetry-modified conformational mapping and classification of the medium rings from crystallographic data. II. exo-unsaturated and heterocyclic seven-membered rings

Allen¹,

Howard²,

Pitchford³

et al. 1994

Acta Crystallogr Sect B

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“…The contribution ratios of the first and second PCs were 0.59 and 0.32 for compound 1 and 0.60 and 0.32 for compound 2, respectively. The high contribution ratios of the first two PCs suggest that there mainly exist only one or two conformational freedoms for the 3D structure of 7-membered rings of compounds 1 and 2 and they probably stem from the geometrical restrictions of 7-membered ring formation 16,17) and three planar non-rotatable bonds (one double bond and two aromatic bonds) in 7-membered rings.…”

Section: Resultsmentioning

confidence: 99%

Monte Carlo Simulations on Atropisomerism of Thienotriazolodiazepines Applicable to Slow Transition Phenomena Using Potential Energy Surfaces by <i>ab initio</i> Molecular Orbital Calculations

Morikami

Itezono

Nishimoto

et al. 2014

CHEMICAL & PHARMACEUTICAL BULLETIN

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Compounds with a medium-sized flexible ring often show atropisomerism that is caused by the highenergy barriers between long-lived conformers that can be isolated and often have different biological properties to each other. In this study, the frequency of the transition between the two stable conformers, aS and aR, of thienotriazolodiazepine compounds with flexible 7-membered rings was estimated computationally by Monte Carlo (MC) simulations and validated experimentally by NMR experiments. To estimate the energy barriers for transitions as precisely as possible, the potential energy (PE) surfaces used in the MC simulations were calculated by molecular orbital (MO) methods. To accomplish the MC simulations with the MObased PE surfaces in a practical central processing unit (CPU) time, the MO-based PE of each conformer was pre-calculated and stored before the MC simulations, and then only referred to during the MC simulations. The activation energies for transitions calculated by the MC simulations agreed well with the experimental ΔG determined by the NMR experiments. The analysis of the transition trajectories of the MC simulations revealed that the transition occurred not only through the transition states, but also through many different transition paths. Our computational methods gave us quantitative estimates of atropisomerism of the thienotriazolodiazepine compounds in a practical period of time, and the method could be applicable for other slow-dynamics phenomena that cannot be investigated by other atomistic simulations.Key words atropisomerism; Monte Carlo simulation; molecular orbital method; diazepine Stereoisomers often show different biological activity, pharmacokinetics and toxicity profiles because a ligand is threedimensionally recognized by biological receptors. Therefore regulatory guidelines, such as Food and Drug Administration (FDA) guidelines, 1) often request information on the biological properties of each stereoisomer in the drug development process. In addition to classical stereoisomers with chiral centers, much attention has been paid recently to the atropisomer. 2-4)A compound which has axial chiralities caused by hindered rotations about rotatable bonds shows atropisomerism. Compounds showing atropisomerism have long-lived (1000 s or longer) conformers that can be isolated, 5) and, like classical stereoisomers, each long-lived conformer often shows different biological activities. 2,3)Atropisomerism is caused by the high energy barrier between long-lived conformers due to the steric and/or electronic repulsions and is often observed in compounds with bulky substituents in the ortho positions. Half lives (t 1/2 ) of the atropisomers are dependent on the energy barriers, thus the degree of atropisomerism is time-dependent.2-5) For compounds with an energy barrier of 120 kJ/mol or higher, the atropisomers have a t 1/2 of several years at room temperature and behave like classical stereoisomers, but when the energy barrier is lower than 80 kJ/mol, the t 1/2 is less than 10 s and compou...

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“…The conformational analysis of cycloheptane has been well documented in the literature (Hendrickson, 1961;Hendrickson, 1967aHendrickson, , 1967bDowd et al, 1970;Pickett & Strauss, 1971;Hendrickson et al, 1973;Bocian et al, 1975;Cremer & Pople, 1975;Flapper & Romers, 1975;Brookeman & Rushworth, 1976;Bocian & Strauss, 1977a, 1977bFlapper et al, 1977;Snyderman et al, 1994;Senderowitz, Guarnieri & Still, 1995;Wiberg, 2003) so it is known that there are five possible distinct conformers being two true minima (twist-chair (TC) and boat (B)) and three first-order transition state (TS) structure, (chair (C), twist-boat (TB) and a third structure named TS3) (Wiberg, 2003). The TC, B and C conformers are depicted in Figure 5.…”

Section: Cycloheptanementioning

confidence: 99%