Timing of elective surgery and risk assessment after SARS-CoV-2 infection: 2023 update: A multidisciplinary consensus statement on behalf of the Association of Anaesthetists, Federation of Surgical Specialty Associations, Royal College of Anaesthetists and Royal College of Surgeons of England.

Guidance for the timing of surgery following SARS-CoV-2 infection needed reassessment given widespread vaccination, less virulent variants, contemporary evidence and a need to increase access to safe surgery. We, therefore, updated previous recommendations to assist policymakers, administrative staff, clinicians and, most importantly, patients. Patients who develop symptoms of SARS-CoV-2 infection within 7 weeks of planned surgery, including on the day of surgery, should be screened for SARS-CoV-2. Elective surgery should not usually be undertaken within 2 weeks of diagnosis of SARS-CoV-2 infection. For patients who have recovered from SARS-CoV-2 infection and who are low risk or having low-risk surgery, most elective surgery can proceed 2 weeks following a SARS-CoV-2 positive test. For patients who are not low risk or having anything other than low-risk surgery between 2 and 7 weeks following infection, an individual risk assessment must be performed. This should consider: patient factors (age; comorbid and functional status); infection factors (severity; ongoing symptoms; vaccination); and surgical factors (clinical priority; risk of disease progression; grade of surgery). This assessment should include the use of an objective and validated risk prediction tool and shared decision-making, taking into account the patient's own attitude to risk. In most circumstances, surgery should proceed unless risk assessment indicates that the risk of proceeding exceeds the risk of delay. There is currently no evidence to support delaying surgery beyond 7 weeks for patients who have fully recovered from or have had mild SARS-CoV-2 infection.

Timing of elective surgery and risk assessment after SARS-CoV-2 infection: an update: A multidisciplinary consensus statement on behalf of the Association of Anaesthetists, Centre for Perioperative Care, Federation of Surgical Specialty Associations, Royal College of Anaesthetists, Royal College of Surgeons of England.

The impact of vaccination and new SARS-CoV-2 variants on peri-operative outcomes is unclear. We aimed to update previously published consensus recommendations on timing of elective surgery after SARS-CoV-2 infection to assist policymakers, administrative staff, clinicians and patients. The guidance remains that patients should avoid elective surgery within 7 weeks of infection, unless the benefits of doing so exceed the risk of waiting. We recommend individualised multidisciplinary risk assessment for patients requiring elective surgery within 7 weeks of SARS-CoV-2 infection. This should include baseline mortality risk calculation and assessment of risk modifiers (patient factors; SARS-CoV-2 infection; surgical factors). Asymptomatic SARS-CoV-2 infection with previous variants increased peri-operative mortality risk three-fold throughout the 6 weeks after infection, and assumptions that asymptomatic or mildly symptomatic omicron SARS-CoV-2 infection does not add risk are currently unfounded. Patients with persistent symptoms and those with moderate-to-severe COVID-19 may require a longer delay than 7 weeks. Elective surgery should not take place within 10 days of diagnosis of SARS-CoV-2 infection, predominantly because the patient may be infectious, which is a risk to surgical pathways, staff and other patients. We now emphasise that timing of surgery should include the assessment of baseline and increased risk, optimising vaccination and functional status, and shared decision-making. While these recommendations focus on the omicron variant and current evidence, the principles may also be of relevance to future variants. As further data emerge, these recommendations may be revised.

SARS-CoV-2 infection, COVID-19 and timing of elective surgery: A multidisciplinary consensus statement on behalf of the Association of Anaesthetists, the Centre for Peri-operative Care, the Federation of Surgical Specialty Associations, the Royal College of Anaesthetists and the Royal College of Surgeons of England.

The scale of the COVID-19 pandemic means that a significant number of patients who have previously been infected with SARS-CoV-2 will require surgery. Given the potential for multisystem involvement, timing of surgery needs to be carefully considered to plan for safe surgery. This consensus statement uses evidence from a systematic review and expert opinion to highlight key principles in the timing of surgery. Shared decision-making regarding timing of surgery after SARS-CoV-2 infection must account for severity of the initial infection; ongoing symptoms of COVID-19; comorbid and functional status; clinical priority and risk of disease progression; and complexity of surgery. For the protection of staff, other patients and the public, planned surgery should not be considered during the period that a patient may be infectious. Precautions should be undertaken to prevent pre- and peri-operative infection, especially in higher risk patients. Elective surgery should not be scheduled within 7 weeks of a diagnosis of SARS-CoV-2 infection unless the risks of deferring surgery outweigh the risk of postoperative morbidity or mortality associated with COVID-19. SARS-CoV-2 causes either transient or asymptomatic disease for most patients, who require no additional precautions beyond a 7-week delay, but those who have persistent symptoms or have been hospitalised require special attention. Patients with persistent symptoms of COVID-19 are at increased risk of postoperative morbidity and mortality even after 7 weeks. The time before surgery should be used for functional assessment, prehabilitation and multidisciplinary optimisation. Vaccination several weeks before surgery will reduce risk to patients and might lessen the risk of nosocomial SARS-CoV-2 infection of other patients and staff. National vaccine committees should consider whether such patients can be prioritised for vaccination. As further data emerge, these recommendations may need to be revised, but the principles presented should be considered to ensure safety of patients, the public and staff.

Redefining q: quaternary ammonium cross sectional area (XSA) as a general descriptor for transport-limiting PTC rate approximations.

The relationships of several key molecular descriptors with the rate of the O'Donnell alkylation under phase transfer catalysis (PTC) have been investigated. The most common parameter used to predict PTC rates, the ammonium ion accessibility, q , is defined in such a way that limits its use to straight-chain tetraalkylammonium catalysts. To find a general descriptor of rate, eight linear, symmetrical tetraalkylammonium cations were examined to determine if a model containing broadly applicable descriptors could be found. The catalytic activity of these salts was determined under PTC conditions (operating under an interfacial, transport-rate limiting mechanism) and was compared with these molecular descriptors. Models could be generated from the ammonium ion accessibility parameter q and the amphiphilic cross sectional area descriptor (XSA), and each gave a correlative model predicting the rate of alkylation. However, a similar model cannot be generated from a descriptor that is a direct measure of ammonium ion accessibility, the solvent accessible ammonium surface area (NC4_SA). These models lead to the conclusion that q must approximate catalyst properties other than ammonium ion accessibility. Additionally, the relationship between XSA and rate demonstrates that XSA approximates the complex behavior of ammonium ions at the interfacial region of a biphasic system, allowing for its use as a general descriptor for transport-limiting PTC rate approximations.

Tandem double intramolecular [4 + 2]/[3 + 2] cycloadditions of nitroalkenes.

[reaction: see text]. A new class of tandem [4 + 2]/[3 + 2] cycloadditions of nitroalkenes is described in which both pericyclic processes are intramolecular. Two subclasses of intra [4 + 2]/intra [3 + 2] cycloadditions have been explored in which the dipolarophile is tethered at either C(5) or C(6) of the nitronate. For both families of precursors, the cycloadditions occur in good yield and are found to be highly regio- and stereoselective. This method converts linear polyenes to functionalized polycyclic systems bearing up to six stereogenic centers.

Highly diastereoselective aldol additions of a chiral ethyl ketone enolate under Lewis base catalysis.

[reaction: see text] The aldol addition of a chiral ethyl ketone enolate bearing an oxygen substituent (OTBS) at the alpha-position proceeds with high internal and relative diastereoselectivities with various achiral aldehydes in good yields. The profound influence of the resident stereogenic center allows for the use of an achiral catalyst, such as HMPA, with minor attenuation in internal stereoselectivity.

Intramolecular hydrosilylation and silicon-assisted cross-coupling: an efficient route to trisubstituted homoallylic alcohols.

[figure: see text] Alkylidenesilacyclopentanes (formed by intramolecular hydrosilylation of homopropargyl alcohols) are efficiently coupled with aryl or alkenyl halides in the presence of tetrabutylammonium fluoride and a palladium(0) catalyst. Yields of cross-coupling were generally high, and the reaction is compatible with a wide range of functional groups. The overall transformation achieves the conversion of homopropargyl alcohols to trisubstituted homoallylic alcohols in a highly stereoselective fashion.

Sequential ring-closing metathesis and silicon-assisted cross-coupling reactions: stereocontrolled synthesis of highly substituted unsaturated alcohols.

A sequential ring-closing metathesis/silicon-assisted cross-coupling sequence has been developed. Alkenyldimethylsilyl ethers of omega-unsaturated alcohols undergo facile ring closure with Schrock's catalyst to afford five-, six-, and seven-membered cycloalkenylsiloxanes bearing substituents on both alkenyl carbons. These siloxanes were highly effective coupling partners with various aryl and alkenyl halides and in the presence of Pd(0) afforded styrenes and dienes in high yield and specificity and with good functional group compatibility.

Synthesis of (+)-1-epiaustraline.

A highly efficient total synthesis of (+)-1-epiaustraline ((+)-1), a tetrahydroxypyrrolizidine alkaloid of the alexine/australine subclass, is described. The key step is a tandem intramolecular [4 + 2]/intermolecular [3 + 2] nitroalkene cycloaddition involving dienylsilyloxy nitroalkene 3 and chiral vinyl ether 4, which establishes four of the five stereocenters present. The final center was installed by a diastereoselective dihydroxylation. Hydrogenolytic unmasking of the nitroso acetal tosylate 17 containing the silyl ether linkage was thwarted by a slow alkylation and an undesired Peterson-type elimination. Prior removal of the silicon moiety by Tamao-Fleming oxidation proceeded in excellent yield and provided a substrate suitable for hydrogenolysis and deprotection. The complete synthesis required only 10 steps to deliver the (+)-1-epiaustraline in 7.0% overall yield.

Highly stereoselective hydrocarbation of terminal alkynes via Pt-catalyzed hydrosilylation/Pd-catalyzed cross-coupling reactions.

[reaction: see text]. The formal addition of an aryl-H or alkenyl-H bond across a terminal alkyne has been accomplished by the combination of platinum-catalyzed hydrosilylation followed by palladium-catalyzed cross-coupling. The use of the t-Bu3P-Pt(DVDS) catalyst in combination with tetramethyldisiloxane gave excellent regio- and stereoselectivity with a number of alkyne substrates. Subsequent, fluoride-promoted cross-coupling proceeded in high yield and stereospecificity for a variety of aryl halides.

Asymmetric catalysis of aldol reactions with chiral lewis bases.

In an extension of studies both on the stereochemical course of the aldol addition and on Lewis-base-catalyzed allylation reactions, we have invented a new Lewis-base-catalyzed asymmetric aldol addition. This Account outlines the conceptual development, the identification of design criteria, and the underlying principles for such a process. The reduction of these elements to practice in the demonstration of enantioselective aldol additions of trichlorosilyl enolates catalyzed by chiral phosphoramides is also presented. From a combination of stereochemical, kinetic, and structural studies, an intruiging mechanistic hypothesis is forwarded that explains the origin of catalysis and diastereoselectivity.

Synthesis of (+)-casuarine.

The first synthesis of (+)-casuarine ((+)-6), a pentahydroxy pyrrolizidine alkaloid of the alexine/australine subclass, is described. The key step is a tandem [4 + 2]/[3 + 2] nitroalkene cycloaddition involving nitrobenzoate 13, chiral vinyl ether 16c, and vinyl silane 10, which establishes five of the six stereocenters present in this potent glycosidase inhibitor. The completion of the synthesis requires only four additional steps to deliver the final product in 20% overall yield.

Synthesis of (-)-7-epiaustraline and (-)-1-epicastanospermine.

Highly efficient and selective syntheses of the title compounds are described. The cornerstone of the synthetic plan is the tandem inter [4 + 2]/inter [3 + 2] cycloaddition process. These syntheses differ from previous applications of this strategy in that they incorporate an alkylation in the hydrogenolysis step to close the second ring of the azabicyclic systems. Notable features of the sequence are (1) the highly regio- and stereoselective [3 + 2] cycloaddition of nitronate 15 with siloxymethyl (Z)-beta-silylvinyl ketone (Z)-22b and (2) the highly selective reduction of the resulting ketone 24a with L-Selectride. A single-crystal X-ray structure analysis of synthetic (-)-7-epiaustraline confirmed that the targeted structure was successfully synthesized. This stimulated a reexamination of the structural assignment of the natural product. (-)-1-Epicastanospermine was synthesized in four steps from the common intermediate 27a. The absolute configuration of (-)-1-epicastanospermine was assured by single-crystal X-ray structure analysis of intermediate (-)-27a. Thus, the sign of the optical rotation had to be revised. The overall efficiency of these syntheses were 9 steps and 23% yield for (-)-7-epiaustraline and 10 steps and 20% yield for (-)-1-epicastanospermine

Synthesis of (+)-casuarine.

[formula: see text] The first synthesis of (+)-casuarine, a pentahydroxy pyrrolizidine alkaloid, is described. The key bond-forming events occur in a tandem [4 + 2]/[3 + 2] nitroalkene cycloaddition involving nitroalkene 6, chiral vinyl ether 7b, and vinyl silane 4. This process also creates five of the six stereocenters present in this potent glycosidase inhibitor. Completion of the synthesis required only four additional steps and delivered (+)-casuarine in 20% overall yield.

(2aS,3S,6S,7S,7bR)-7-[(dimethylphenyl)-silyl]-2-oxo-6-[(1R,2S)-2- phenylcyclo-hexyloxy]-2a,3,6,7,7a,7b-hexahydro-2H-1,4,5-trioxa-4a- azacyclopenta[cd]indene-3-carboxylic acid 1-methylethyl ester.

The structure of the title compound, C31H39NO7Si, was determined and found to be a fused tricyclic nitroso acetal. Remarkable features include a twist-boat conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [Sigma (angles) = 310.6(6) degrees]. Three of the contiguous stereocenters in the nitroso acetal are of the same correct relative and absolute configuration as is found in (+)-crotanecine.

rel-(1R,6S,7S,8R,9S)-9-methyl-8-phenyl-6-[(1s,2R)-(2-phenylcyclohexyl) oxy]-4-aza-3,5-dioxatricyclo[5.2.1.0(4,9)]decane.

The structure of the title compound, C26H31NO3, was determined by X-ray crystallography. It was found to be a unique bridged tricyclic nitroso acetal. Notable features include a chair conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [sigma angles = 314.2 (6) degrees]. The configurations of the five contiguous stereogenic centers in the nitroso acetal establish that the tandem cycloaddition sequence proceeded via an exo-[4 + 2] endo-[3 + 2] pathway.