May 2019

Preliminary Pricing Supplement

Dated April 29, 2019

Registration Statement No. 333-225551

Filed pursuant to Rule 424(b)(2)

(To Prospectus dated October 31, 2018

and Product Supplement dated October 31, 2018)

▪    If, on any determination date, the closing price or the final price is equal to or greater than the downside threshold level, we will pay a contingent payment of $0.50 (equivalent to 20.00% per annum of the stated principal amount) per security on the related contingent payment date.

▪    If, on any determination date, the closing price or the final price is less than the downside threshold level, no contingent payment will be made with respect to that determination date.

$·, which is equal to the closing price of the underlying equity on the pricing date

(as may be adjusted in the case of certain adjustment events as described under “General Terms of the Securities — Antidilution Adjustments for Securities Linked to an Underlying Equity or Equity Basket Asset” and “— Reorganization Events for Securities Linked to an Underlying Equity or Equity Basket Asset” in the accompanying product supplement).

2.00%^(a)

+ 0.50%^(b)

2.50%

Product supplement dated October 31, 2018

On any determination date other than the final determination date, the closing price is equal to or greater than the call threshold level.

▪   The securities will be automatically redeemed early for an early redemption amount equal to (i) the stated principal amount plus (ii) the contingent payment with respect to the related determination date.

▪   Investors will not participate in any appreciation of the underlying equity from the initial price.

The securities are not automatically redeemed early and the final price is equal to or greater than the downside threshold level.

▪   The payment due at maturity will be (i) the stated principal amount plus (ii) any contingent payment with respect to the final determination date.

▪   Investors will not participate in any appreciation of the underlying equity from the initial price.

The securities are not automatically redeemed early and the final price is less than the downside threshold level.

▪   The payment due at maturity will be the cash value.

▪   Investors will lose a significant portion and may lose all of their initial investment in this scenario.

The Common Stock of Tesla, Inc. –
Daily Closing Prices June 29, 2010 to April 25, 2019

The U.S. federal income tax consequences of your investment in the securities are uncertain. There are no statutory provisions, regulations, published rulings or judicial decisions addressing the characterization for U.S. federal income tax purposes of securities with terms that are substantially the same as the securities. Some of these tax consequences are summarized below, but we urge you to read the more detailed discussion in “Material U.S. Federal Income Tax Consequences”, including the section “— Securities Treated as Prepaid Derivatives or Prepaid Forwards with Associated Contingent Coupons”, in the accompanying product supplement and to discuss the tax consequences of your particular situation with your tax advisor. This discussion is based upon the Internal Revenue Code of 1986, as amended (the “Code”), final, temporary and proposed U.S. Treasury Department (the “Treasury”) regulations, rulings and decisions, in each case, as available and in effect as of the date hereof, all of which are subject to change, possibly with retroactive effect. Tax consequences under state, local and non-U.S. laws are not addressed herein. No ruling from the U.S. Internal Revenue Service (the “IRS”) has been sought as to the U.S. federal income tax consequences of your investment in the Securities, and the following discussion is not binding on the IRS.

U.S. Tax Treatment. Pursuant to the terms of the securities, UBS and you agree, in the absence of a statutory or regulatory change or an administrative determination or judicial ruling to the contrary, to characterize the securities as prepaid derivative contracts with respect to the underlying equity. If your securities are so treated, any contingent payment that is paid by UBS (including on the maturity date or upon early redemption) should be included in your income as ordinary income in accordance with your regular method of accounting for U.S. federal income tax purposes.

In addition, excluding amounts attributable to any contingent payment, you should generally recognize capital gain or loss upon the taxable disposition of your securities in an amount equal to the difference between the amount you receive at such time (other than amounts or proceeds attributable to a contingent payment or any amount attributable to any accrued but unpaid contingent payment) and the amount you paid for your securities. Such gain or loss should generally be long-term capital gain or loss if you have held your securities for more than one year (otherwise such gain or loss should be short-term capital gain or loss). The deductibility of capital losses is subject to limitations. Although uncertain, it is possible that proceeds received from the sale or exchange of your securities prior to a contingent payment date, but that could be attributed to an expected contingent payment, could be treated as ordinary income. You should consult your tax advisor regarding this risk.

Based on certain factual representations received from us, our counsel, Cadwalader, Wickersham & Taft LLP, is of the opinion that it would be reasonable to treat your securities in the manner described above. However, because there is no authority that specifically addresses the tax treatment of the securities, it is possible that your securities could alternatively be treated for tax purposes as a single contingent payment debt instrument, or pursuant to some other characterization, such that the timing and character of your income from the securities could differ materially and adversely from the treatment described above, as described further under “Material U.S. Federal Income Tax Consequences”, including the section “— Securities Treated as Prepaid Derivatives or Prepaid Forwards with Associated Contingent Coupons”, in the accompanying product supplement.

Except to the extent otherwise required by law, UBS intends to treat your Securities for U.S. federal income tax purposes in accordance with the treatment described above and under “Material U.S. Federal Income Tax Consequences”, including the section “— Securities Treated as Prepaid Derivatives or Prepaid Forwards with Associated Contingent Coupons”, in the

accompanying product supplement unless and until such time as the IRS and the Treasury determine that some other treatment is more appropriate.

Notice 2008-2. In 2007, the IRS released a notice that may affect the taxation of holders of the securities. According to Notice 2008-2, the IRS and the Treasury are actively considering whether the holder of an instrument such as the securities should be required to accrue ordinary income on a current basis. It is not possible to determine what guidance they will ultimately issue, if any. It is possible, however, that under such guidance, holders of the securities will ultimately be required to accrue income currently in excess of any receipt of contingent payments and this could be applied on a retroactive basis. The IRS and the Treasury are also considering other relevant issues, including whether additional gain or loss from such instruments should be treated as ordinary or capital, whether non-U.S. holders of such instruments should be subject to withholding tax on any deemed income accruals, and whether the special “constructive ownership rules” of Section 1260 of the Code should be applied to such instruments. Both U.S. and non-U.S. holders are urged to consult their tax advisors concerning the significance and potential impact of the above considerations.

Medicare Tax on Net Investment Income. U.S. holders that are individuals, estates or certain trusts are subject to an additional 3.8% tax on all or a portion of their “net investment income,” which may include any income or gain realized with respect to the securities, to the extent of their net investment income that when added to their other modified adjusted gross income, exceeds $200,000 for an unmarried individual, $250,000 for a married taxpayer filing a joint return (or a surviving spouse), $125,000 for a married individual filing a separate return or the dollar amount at which the highest tax bracket begins for an estate or trust. The 3.8% Medicare tax is determined in a different manner than the income tax. You should consult your tax advisor as to the consequences of the 3.8% Medicare tax with respect to your investment in the securities.

Specified Foreign Financial Assets. Certain U.S. holders that own “specified foreign financial assets” in excess of an applicable threshold may be subject to reporting obligations with respect to such assets with their tax returns, especially if such assets are held outside the custody of a U.S. financial institution. You are urged to consult your tax advisor as to the application of this legislation to your ownership of the securities.

Non-U.S. Holders. The U.S. federal income tax treatment of the contingent payments is unclear. Subject to Section 871(m) of the Code and FATCA, as discussed below, our counsel is of the opinion that contingent payments paid to a non-U.S. holder that provides us (and/or the applicable withholding agent) with a fully completed and validly executed applicable IRS Form W-8 should not be subject to U.S. withholding tax and we do not intend to withhold any tax on contingent payments. However, it is possible that the IRS could assert that such payments are subject to U.S. withholding tax, or that another withholding agent may otherwise determine that withholding is required, in which case we or the other withholding agent may withhold up to 30% on such payments (subject to reduction or elimination of such withholding tax pursuant to an applicable income tax treaty). We will not pay any additional amounts in respect of such withholding. Subject to Section 897 of the Code and Section 871(m) of the Code, discussed below, gain from the taxable disposition of a security generally should not be subject to U.S. tax unless (i) such gain is effectively connected with a trade or business conducted by the non-U.S. holder in the U.S., (ii) the non-U.S. holder is a non-resident alien individual and is present in the U.S. for 183 days or more during the taxable year of such taxable disposition and certain other conditions are satisfied, or (iii) the non-U.S. holder has certain other present or former connections with the U.S.

Section 897. We will not attempt to ascertain whether the underlying equity issuer would be treated as a “United States real property holding corporation” (“USRPHC”) within the meaning of Section 897 of the Code. We also have not attempted to determine whether the securities should be treated as “United States real property interests” (“USRPI”) as defined in Section 897 of the Code. If the underlying equity issuer and the securities were so treated, certain adverse U.S. federal income tax consequences could possibly apply, including subjecting any gain to a non-U.S. holder in respect of a security upon a taxable disposition of the security to the U.S. federal income tax on a net basis, and the proceeds from such a taxable disposition to a 15% withholding tax. You should consult your tax advisor regarding the potential treatment of the underlying equity issuer as a USRPHC and the securities as USRPI.

Section 871(m). A 30% withholding tax (which may be reduced by an applicable income tax treaty) is imposed under Section 871(m) of the Code on certain “dividend equivalents” paid or

deemed paid to a non-U.S. holder with respect to a “specified equity-linked instrument” that references one or more dividend-paying U.S. equity securities. The withholding tax can apply even if the instrument does not provide for payments that reference dividends. Treasury regulations provide that the withholding tax applies to all dividend equivalents paid or deemed paid on specified equity-linked instruments that have a delta of one (“delta one specified equity-linked instruments”) issued after 2016 and to all dividend equivalents paid or deemed paid on all other specified equity-linked instruments issued after 2018. However, the IRS has issued guidance that states that the Treasury and the IRS intend to amend the effective dates of the Treasury regulations to provide that withholding on dividend equivalents paid or deemed paid will not apply to specified equity-linked instruments that are not delta-one specified equity-linked instruments and are issued before January 1, 2021.

Based on our determination that the securities are not “delta-one” with respect to the underlying equity, our counsel is of the opinion that the securities should not be delta-one specified equity-linked instruments and thus should not be subject to withholding on dividend equivalents. Our determination is not binding on the IRS, and the IRS may disagree with this determination. Furthermore, the application of Section 871(m) of the Code will depend on our determinations made upon issuance of the securities. If withholding is required, we will not make payments of any additional amounts.

Nevertheless, after issuance, it is possible that your securities could be deemed to be reissued for tax purposes upon the occurrence of certain events affecting the underlying equity or your securities, and following such occurrence your securities could be treated as delta-one specified equity-linked instruments that are subject to withholding on dividend equivalents. It is also possible that withholding tax or other tax under Section 871(m) of the Code could apply to the securities under these rules if you enter, or have entered, into certain other transactions in respect of the underlying equity or the securities. If you enter, or have entered, into other transactions in respect of the underlying equity or the securities, you should consult your tax advisor regarding the application of Section 871(m) of the Code to your securities in the context of your other transactions.

Because of the uncertainty regarding the application of the 30% withholding tax on dividend equivalents to the securities, you are urged to consult your tax advisor regarding the potential application of Section 871(m) of the Code and the 30% withholding tax to an investment in the securities.

Foreign Account Tax Compliance Act. Legislation commonly referred to as the Foreign Account Tax Compliance Act (“FATCA”) generally imposes a withholding tax of 30% on payments to certain non-U.S. entities (including financial intermediaries) with respect to certain financial instruments, unless various U.S. information reporting and due diligence requirements have been satisfied. An intergovernmental agreement between the U.S. and the non-U.S. entity’s jurisdiction may modify these requirements. This legislation generally applies to certain financial instruments that are treated as paying U.S.-source interest or other U.S.-source “fixed or determinable annual or periodical” income (“FDAP income”). Withholding (if applicable) applies to payments of U.S.-source FDAP income but, pursuant to certain Treasury regulations and IRS guidance, does not apply to payments of gross proceeds on the disposition (including upon retirement) of financial instruments. As the treatment of the securities is unclear, it is possible that any contingent payment with respect to the securities could be subject to the FATCA rules. If withholding applies to the securities, we will not be required to pay any additional amounts with respect to amounts withheld. Both U.S. and non-U.S. holders should consult their tax advisors regarding the potential application of FATCA to the securities.

Proposed Legislation. In 2007, legislation was introduced in Congress that, if it had been enacted, would have required holders of securities similar to the securities purchased after the bill was enacted to accrue interest income over the term of such securities despite the fact that there may be no interest payments over the term of such securities.

Furthermore, in 2013, the House Ways and Means Committee released in draft form certain proposed legislation relating to financial instruments. If it had been enacted, the effect of this legislation generally would have been to require instruments such as the securities to be marked to market on an annual basis with all gains and losses to be treated as ordinary, subject to certain exceptions.

It is not possible to predict whether any similar or identical bills will be enacted in the future, or whether any such bill would affect the tax treatment of your securities. You are urged to consult

your tax advisor regarding the possible changes in law and their possible impact on the tax treatment of your securities.

Both U.S. and non-U.S. holders are urged to consult their tax advisors concerning the application of U.S. federal income tax laws to their particular situations, as well as any tax consequences of the purchase, beneficial ownership and disposition of the securities arising under the laws of any state, local, non-U.S. or other taxing jurisdiction.

We will use the net proceeds we receive from the sale of the securities for the purposes we describe in the accompanying prospectus under “Use of Proceeds and Hedging.” We and/or our affiliates may also use those proceeds in transactions intended to hedge our obligations under the securities as described below.

In connection with the sale of the securities, we and/or our affiliates may enter into hedging transactions involving the execution of long-term or short-term interest rate swaps, futures and option transactions or purchases and sales of securities before, on and after the pricing date of the securities. From time to time, we and/or our affiliates may enter into additional hedging transactions or unwind those we have entered into.

We and/or our affiliates may acquire a long or short position in securities similar to the securities from time to time and may, in our or their sole discretion, hold or resell those securities.

The hedging activity discussed above may adversely affect the market value of the securities from time to time and payment on the securities, including any payment at maturity. See “Risk Factors” beginning on page 10 of this document for a discussion of these adverse effects.

Pursuant to the terms of a distribution agreement, UBS will agree to sell to UBS Securities LLC, and UBS Securities LLC will agree to purchase from UBS, the stated principal amount of the securities specified on the front cover of this document at the price to public less a fee of $0.25 per $10.00 stated principal amount of securities. UBS Securities LLC will agree to resell all of the securities to Morgan Stanley Wealth Management with an underwriting discount of $0.25 reflecting a fixed structuring fee of $0.05 and a fixed sales commission of $0.20 per $10.00 stated principal amount of securities that Morgan Stanley Wealth Management sells.

UBS, UBS Securities LLC or any other affiliate of UBS may use this document, the accompanying product supplement and the accompanying prospectus in a market-making transaction for any securities after their initial sale. In connection with the offering, UBS, UBS Securities LLC, any other affiliate of UBS or any other securities dealers may distribute this document, the accompanying product supplement and the accompanying prospectus electronically. Unless UBS or its agent informs the purchaser otherwise in the confirmation of sale, this document, the accompanying product supplement and the accompanying prospectus are being used in a market-making transaction.

Conflicts of Interest — UBS Securities LLC is an affiliate of UBS and, as such, has a “conflict of interest” in this offering within the meaning of Financial Industry Regulatory Authority, Inc. (“FINRA”) Rule 5121. In addition, UBS will receive the net proceeds (excluding the underwriting discount) from the initial public offering of the securities and, thus creates an additional conflict of interest within the meaning of FINRA Rule 5121. UBS Securities LLC is not permitted to sell securities in this offering to an account over which it exercises discretionary authority without the prior specific written approval of the account holder.

UBS Securities LLC and its affiliates may offer to buy or sell the securities in the secondary market (if any) at prices greater than UBS’ internal valuation — The value of the securities at any time will vary based on many factors that cannot be predicted. However, the price (not including UBS Securities LLC’s or any affiliate’s customary bid-ask spreads) at which UBS Securities LLC or any affiliate would offer to buy or sell the securities immediately after the pricing date in the secondary market is expected to exceed the estimated initial value of the securities as determined by reference to our internal pricing models. The amount of the excess will decline to zero on a straight line basis over a period ending no later than 6 weeks after the pricing date, provided that UBS Securities LLC may shorten the period based on various factors, including the magnitude of purchases and other negotiated provisions with selling agents. Notwithstanding the foregoing, UBS Securities LLC and its affiliates are not required to make a market for the securities and may stop making a market at any time. For more information about secondary market offers and the estimated initial value of the securities, see “Risk Factors — Fair value considerations” and “— Limited or no secondary market and secondary market price considerations” beginning on pages 10 and 11 of this document.